Uno Platform Compatibility updates (#3651)

## PR Type
What kind of change does this PR introduce?
- Refactoring (no functional changes, no api changes) 

## What is the new behavior?

This PR adds a set of forward compatibilty changes to ease the cross-compilation of the community toolkit to Uno Platform targets.

- Partials are needed for code generation
- Use `TargetFrameworks` instead of `TargetFramework` to allow for late modification of the platform list

## PR Checklist

Please check if your PR fulfills the following requirements:

- [ ] Tested code with current [supported SDKs](../readme.md#supported)
- [ ] Pull Request has been submitted to the documentation repository [instructions](..\contributing.md#docs). Link: <!-- docs PR link -->
- [ ] Sample in sample app has been added / updated (for bug fixes / features)
    - [ ] Icon has been created (if new sample) following the [Thumbnail Style Guide and templates](https://github.com/windows-toolkit/WindowsCommunityToolkit-design-assets)
- [ ] New major technical changes in the toolkit have or will be added to the [Wiki](https://github.com/windows-toolkit/WindowsCommunityToolkit/wiki) e.g. build changes, source generators, testing infrastructure, sample creation changes, etc...
- [ ] Tests for the changes have been added (for bug fixes / features) (if applicable)
- [ ] Header has been added to all new source files (run *build/UpdateHeaders.bat*)
- [x] Contains **NO** breaking changes

<!-- If this PR contains a breaking change, please describe the impact and migration path for existing applications below. 
     Please note that breaking changes are likely to be rejected within minor release cycles or held until major versions. -->


## Other information

Author: msftbot[bot]

Microsoft.Toolkit.Uwp.Connectivity/Microsoft.Toolkit.Uwp.Connectivity.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="MSBuild.Sdk.Extras">
 
   <PropertyGroup>
-    <TargetFramework>uap10.0.17763</TargetFramework>
+    <TargetFrameworks>uap10.0.17763</TargetFrameworks>
     <Title>Windows Community Toolkit Devices</Title>
     <Description>This library enables easier consumption of connectivity Devices/Peripherals and handle its connection to Windows devices. It contains BluetoothLE and Network connectivity helpers.</Description>
     <PackageTags>UWP Toolkit Windows Devices Bluetooth BluetoothLE BLE Networking</PackageTags>

Microsoft.Toolkit.Uwp.DeveloperTools/AlignmentGrid/AlignmentGrid.cs

@@ -12,7 +12,7 @@ namespace Microsoft.Toolkit.Uwp.DeveloperTools
     /// <summary>
     /// AlignmentGrid is used to display a grid to help aligning controls
     /// </summary>
-    public class AlignmentGrid : ContentControl
+    public partial class AlignmentGrid : ContentControl
     {
         /// <summary>
         /// Identifies the <see cref="LineBrush"/> dependency property.

Microsoft.Toolkit.Uwp.DeveloperTools/FocusTracker/FocusTracker.cs

@@ -24,7 +24,7 @@ namespace Microsoft.Toolkit.Uwp.DeveloperTools
     [TemplatePart(Name = "ControlType", Type = typeof(TextBlock))]
     [TemplatePart(Name = "ControlAutomationName", Type = typeof(TextBlock))]
     [TemplatePart(Name = "ControlFirstParentWithName", Type = typeof(TextBlock))]
-    public class FocusTracker : Control
+    public partial class FocusTracker : Control
     {
         /// <summary>
         /// Defines the <see cref="IsActive"/> dependency property.

Microsoft.Toolkit.Uwp.DeveloperTools/Microsoft.Toolkit.Uwp.DeveloperTools.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="MSBuild.Sdk.Extras">
 
   <PropertyGroup>
-    <TargetFramework>uap10.0.17763</TargetFramework>
+    <TargetFrameworks>uap10.0.17763</TargetFrameworks>
     <Title>Windows Community Toolkit Developer Tools</Title>
     <Description>This library provides XAML user controls and services to help developers build their app. It is part of the Windows Community Toolkit.
 

Microsoft.Toolkit.Uwp.UI.Animations/CompositionAnimations/Animations/AnimationBase.cs

@@ -14,7 +14,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Animations
     /// Abstract class providing common dependency properties for composition animations
     /// </summary>
     [ContentProperty(Name = nameof(KeyFrames))]
-    public abstract class AnimationBase : DependencyObject
+    public abstract partial class AnimationBase : DependencyObject
     {
         /// <summary>
         /// Identifies the <see cref="Target"/> property

Microsoft.Toolkit.Uwp.UI.Animations/CompositionAnimations/KeyFrames/KeyFrame.cs

@@ -9,7 +9,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Animations
     /// <summary>
     /// Provides common Dependency properties for KeyFrames
     /// </summary>
-    public abstract class KeyFrame : DependencyObject
+    public abstract partial class KeyFrame : DependencyObject
     {
         /// <summary>
         /// Identifies the <see cref="Key"/> dependency property

Microsoft.Toolkit.Uwp.UI.Animations/Extensions/AnimationTools.cs

@@ -9,7 +9,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Animations
     /// <summary>
     /// Internal tool to link composite transforms to elements
     /// </summary>
-    internal class AnimationTools : DependencyObject
+    internal partial class AnimationTools : DependencyObject
     {
         /// <summary>
         /// Attached property used to link composite transform with UIElement

Microsoft.Toolkit.Uwp.UI.Animations/Microsoft.Toolkit.Uwp.UI.Animations.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="MSBuild.Sdk.Extras">
 
   <PropertyGroup>
-    <TargetFramework>uap10.0.17763</TargetFramework>
+    <TargetFrameworks>uap10.0.17763</TargetFrameworks>
     <Title>Windows Community Toolkit Animations</Title>
     <Description>
       This library provides helpers and extensions on top of Windows Composition and XAML storyboards. It is part of the Windows Community Toolkit.

Microsoft.Toolkit.Uwp.UI.Controls.DataGrid/Microsoft.Toolkit.Uwp.UI.Controls.DataGrid.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="MSBuild.Sdk.Extras">
   <PropertyGroup>
-    <TargetFramework>uap10.0.17763</TargetFramework>
+    <TargetFrameworks>uap10.0.17763</TargetFrameworks>
     <Title>Windows Community Toolkit Controls DataGrid</Title>
     <Description>
       This library provides a XAML DataGrid control. It is part of the Windows Community Toolkit.

Microsoft.Toolkit.Uwp.UI.Controls.Layout/Microsoft.Toolkit.Uwp.UI.Controls.Layout.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="MSBuild.Sdk.Extras">
 
   <PropertyGroup>
-    <TargetFramework>uap10.0.17763</TargetFramework>
+    <TargetFrameworks>uap10.0.17763</TargetFrameworks>
     <TargetPlatformVersion Condition="'$(TargetPlatformVersion)' == '' ">10.0.19041.0</TargetPlatformVersion>
     <Title>Windows Community Toolkit Layout</Title>
     <Description>

Microsoft.Toolkit.Uwp.UI.Controls.Markdown/Microsoft.Toolkit.Uwp.UI.Controls.Markdown.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="MSBuild.Sdk.Extras">
   <PropertyGroup>
-    <TargetFramework>uap10.0.17763</TargetFramework>
+    <TargetFrameworks>uap10.0.17763</TargetFrameworks>
     <Title>Windows Community Toolkit Controls Markdown</Title>
     <Description>
       This library provides a XAML MarkdownTextBlock control, an efficient and extensible control that can parse and render markdown. It is part of the Windows Community Toolkit.

Microsoft.Toolkit.Uwp.UI.Controls/Carousel/Carousel.cs

@@ -20,7 +20,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls
     /// <summary>
     /// A modern UI Carousel control. Really flexible. Works with touch, keyboard, mouse.
     /// </summary>
-    public class Carousel : ItemsControl
+    public partial class Carousel : ItemsControl
     {
         /// <summary>
         /// Gets or sets the selected item.

Microsoft.Toolkit.Uwp.UI.Controls/Carousel/CarouselItem.cs

@@ -13,7 +13,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls
     /// <summary>
     /// Represents the container for an item in a Carousel control.
     /// </summary>
-    public class CarouselItem : SelectorItem
+    public partial class CarouselItem : SelectorItem
     {
         private const string PointerOverState = "PointerOver";
         private const string PointerOverSelectedState = "PointerOverSelected";

Microsoft.Toolkit.Uwp.UI.Controls/Carousel/CarouselPanel.cs

@@ -18,7 +18,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls
     /// <summary>
     /// The panel used in the <see cref="Carousel"/> control
     /// </summary>
-    public class CarouselPanel : Panel
+    public partial class CarouselPanel : Panel
     {
         // Storyboard on gesture
         private Storyboard storyboard = new Storyboard();

Microsoft.Toolkit.Uwp.UI.Controls/ColorPicker/ColorPickerButton.cs

@@ -17,7 +17,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls
     /// A <see cref="DropDownButton"/> which displays a color as its <c>Content</c> and it's <c>Flyout</c> is a <see cref="ColorPicker"/>.
     /// </summary>
     [TemplatePart(Name = nameof(CheckeredBackgroundBorder), Type = typeof(Border))]
-    public class ColorPickerButton : DropDownButton
+    public partial class ColorPickerButton : DropDownButton
     {
         /// <summary>
         /// Gets the <see cref="Controls.ColorPicker"/> instances contained by the <see cref="DropDownButton"/>.

Microsoft.Toolkit.Uwp.UI.Controls/HeaderedContentControl/HeaderedContentControl.cs

@@ -10,7 +10,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls
     /// <summary>
     /// Provides the base implementation for all controls that contain single content and have a header.
     /// </summary>
-    public class HeaderedContentControl : ContentControl
+    public partial class HeaderedContentControl : ContentControl
     {
         private const string PartHeaderPresenter = "HeaderPresenter";
 

Microsoft.Toolkit.Uwp.UI.Controls/HeaderedItemsControl/HeaderedItemsControl.cs

@@ -10,7 +10,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls
     /// <summary>
     /// Represents a control that contains multiple items and has a header.
     /// </summary>
-    public class HeaderedItemsControl : ItemsControl
+    public partial class HeaderedItemsControl : ItemsControl
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="HeaderedItemsControl"/> class.

Microsoft.Toolkit.Uwp.UI.Controls/LayoutTransformControl/PropertyChangeEventSource.cs

@@ -12,7 +12,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls
     /// Allows raise an event when the value of a dependency property changes when a view model is otherwise not necessary.
     /// </summary>
     /// <typeparam name="TPropertyType">Type of the DependencyProperty</typeparam>
-    internal class PropertyChangeEventSource<TPropertyType> : FrameworkElement
+    internal partial class PropertyChangeEventSource<TPropertyType> : FrameworkElement
     {
         private readonly DependencyObject _source;
 

Microsoft.Toolkit.Uwp.UI.Controls/Microsoft.Toolkit.Uwp.UI.Controls.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="MSBuild.Sdk.Extras">
 
   <PropertyGroup>
-    <TargetFramework>uap10.0.17763</TargetFramework>
+    <TargetFrameworks>uap10.0.17763</TargetFrameworks>
     <Title>Windows Community Toolkit Controls</Title>
     <Description>
       This library provides XAML templated controls. It is part of the Windows Community Toolkit.

Microsoft.Toolkit.Uwp.UI.Controls/OrbitView/OrbitView.cs

@@ -24,7 +24,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls
     [TemplatePart(Name = "AnchorCanvas", Type = typeof(Canvas))]
     [TemplatePart(Name = "OrbitGrid", Type = typeof(Grid))]
     [TemplatePart(Name = "CenterContent", Type = typeof(ContentPresenter))]
-    public class OrbitView : ItemsControl
+    public partial class OrbitView : ItemsControl
     {
         private const double AnimationDuration = 200;
 

Microsoft.Toolkit.Uwp.UI.Controls/OrbitView/OrbitViewDataItem.cs

@@ -11,7 +11,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls
     /// <summary>
     /// A class that can be used to provide data context for <see cref="OrbitView"></see> items by providing distance and diameter values
     /// </summary>
-    public class OrbitViewDataItem : DependencyObject
+    public partial class OrbitViewDataItem : DependencyObject
     {
         /// <summary>
         /// Gets or sets a value indicating the distance from the center.

Microsoft.Toolkit.Uwp.UI.Controls/OrbitView/OrbitViewItem.cs

@@ -17,7 +17,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls
     [TemplateVisualState(Name = VsNormal, GroupName = CommonStateGroup)]
     [TemplateVisualState(Name = VsPressed, GroupName = CommonStateGroup)]
     [TemplateVisualState(Name = VsPointerOver, GroupName = CommonStateGroup)]
-    public class OrbitViewItem : ContentControl
+    public partial class OrbitViewItem : ContentControl
     {
         private const string CommonStateGroup = "CommonStates";
         private const string VsNormal = "Normal";

Microsoft.Toolkit.Uwp.UI.Controls/RadialProgressBar/RadialProgressBar.cs

@@ -19,7 +19,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls
     [TemplatePart(Name = OutlineArcPartName, Type = typeof(ArcSegment))]
     [TemplatePart(Name = BarFigurePartName, Type = typeof(PathFigure))]
     [TemplatePart(Name = BarArcPartName, Type = typeof(ArcSegment))]
-    public class RadialProgressBar : ProgressBar
+    public partial class RadialProgressBar : ProgressBar
     {
         private const string OutlineFigurePartName = "OutlineFigurePart";
         private const string OutlineArcPartName = "OutlineArcPart";

Microsoft.Toolkit.Uwp.UI.Controls/RemoteDevicePicker/RemoteDevicePicker.cs

@@ -25,7 +25,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls
     [TemplatePart(Name = "StatusType", Type = typeof(ComboBox))]
     [TemplatePart(Name = "AuthorizationType", Type = typeof(ComboBox))]
     [TemplatePart(Name = "AdvancedFiltersGrid", Type = typeof(Grid))]
-    public sealed class RemoteDevicePicker : ContentDialog
+    public sealed partial class RemoteDevicePicker : ContentDialog
     {
         private ListView _listDevices;
         private ComboBox _listDeviceTypes;

Microsoft.Toolkit.Uwp.UI.Controls/RotatorTile/RotatorTile.cs

@@ -23,7 +23,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls
     [TemplatePart(Name = NextPartName, Type = typeof(FrameworkElement))]
     [TemplatePart(Name = TranslatePartName, Type = typeof(TranslateTransform))]
     [TemplatePart(Name = StackPartName, Type = typeof(StackPanel))]
-    public class RotatorTile : Control
+    public partial class RotatorTile : Control
     {
         private const string ScrollerPartName = "Scroller";
         private const string CurrentPartName = "Current";

Microsoft.Toolkit.Uwp.UI.Controls/ScrollHeader/ScrollHeader.cs

@@ -14,7 +14,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls
     /// <summary>
     /// Scroll header control to be used with ListViews or GridViews
     /// </summary>
-    public class ScrollHeader : ContentControl
+    public partial class ScrollHeader : ContentControl
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="ScrollHeader"/> class.

Microsoft.Toolkit.Uwp.UI.Controls/SwitchPresenter/Case.cs

@@ -12,7 +12,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls
     /// <see cref="Case"/> is the value container for the <see cref="SwitchPresenter"/>.
     /// </summary>
     [ContentProperty(Name = nameof(Content))]
-    public class Case : DependencyObject
+    public partial class Case : DependencyObject
     {
         internal SwitchPresenter Parent { get; set; } // TODO: Can we remove Parent need here and just use events?
 

Microsoft.Toolkit.Uwp.UI.Controls/SwitchPresenter/SwitchPresenter.cs

@@ -15,7 +15,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls
     /// When provided a set of <see cref="Case"/>s and a <see cref="Value"/>, it will pick the matching <see cref="Case"/> with the corresponding <see cref="Case.Value"/>.
     /// </summary>
     [ContentProperty(Name = nameof(SwitchCases))]
-    public sealed class SwitchPresenter : ContentPresenter
+    public sealed partial class SwitchPresenter : ContentPresenter
     {
         /// <summary>
         /// Gets the current <see cref="Case"/> which is being displayed.

Microsoft.Toolkit.Uwp.UI.Controls/TextToolbar/Symbols/List.cs

@@ -7,7 +7,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls.TextToolbarSymbols
     /// <summary>
     /// Creates a List Icon
     /// </summary>
-    public class List : Symbol
+    public partial class List : Symbol
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="List"/> class.

Microsoft.Toolkit.Uwp.UI.Controls/TextToolbar/Symbols/NumberedList.cs

@@ -7,7 +7,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls.TextToolbarSymbols
     /// <summary>
     /// Creates a Numbered List Icon
     /// </summary>
-    public class NumberedList : Symbol
+    public partial class NumberedList : Symbol
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="NumberedList"/> class.

Microsoft.Toolkit.Uwp.UI.Controls/TextToolbar/Symbols/Symbol.cs

@@ -13,7 +13,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls.TextToolbarSymbols
     /// </summary>
     [TemplateVisualState(GroupName = Common, Name = Normal)]
     [TemplateVisualState(GroupName = Common, Name = Disabled)]
-    public abstract class Symbol : Control
+    public abstract partial class Symbol : Control
     {
         internal const string Common = "CommonStates";
         internal const string Normal = "Normal";

Microsoft.Toolkit.Uwp.UI.Controls/TextToolbar/ToolbarItems/DefaultButton.cs

@@ -9,7 +9,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls.TextToolbarButtons
     /// <summary>
     /// Specifies a DefaultButton, modifies a Button Instance
     /// </summary>
-    public class DefaultButton : DependencyObject
+    public partial class DefaultButton : DependencyObject
     {
         /// <summary>
         /// Identifies the <see cref="IsVisible"/> dependency property.

Microsoft.Toolkit.Uwp.UI.Controls/TextToolbar/ToolbarItems/ToolbarButton.cs

@@ -14,7 +14,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls.TextToolbarButtons
     /// <summary>
     /// An Interactive button in the TextToolbar, to perform a formatting task.
     /// </summary>
-    public class ToolbarButton : AppBarButton, IToolbarItem, INotifyPropertyChanged
+    public partial class ToolbarButton : AppBarButton, IToolbarItem, INotifyPropertyChanged
     {
         /// <summary>
         /// Identifies the <see cref="ToolTip"/> dependency property.
@@ -164,6 +164,7 @@ public int Position
             set
             {
                 _position = value;
+
                 PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Position)));
             }
         }

Microsoft.Toolkit.Uwp.UI.Controls/TextToolbar/ToolbarItems/ToolbarSeparator.cs

@@ -9,7 +9,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Controls.TextToolbarButtons
     /// <summary>
     /// Separates a collection of <see cref="IToolbarItem"/>
     /// </summary>
-    public class ToolbarSeparator : AppBarSeparator, IToolbarItem
+    public partial class ToolbarSeparator : AppBarSeparator, IToolbarItem
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="ToolbarSeparator"/> class.

Microsoft.Toolkit.Uwp.UI.Controls/TokenizingTextBox/PretokenStringContainer.cs

@@ -6,7 +6,10 @@
 
 namespace Microsoft.Toolkit.Uwp.UI.Controls
 {
-    internal class PretokenStringContainer : DependencyObject, ITokenStringContainer
+    /// <summary>
+    /// <see cref="TokenizingTextBox"/> support class
+    /// </summary>
+    internal partial class PretokenStringContainer : DependencyObject, ITokenStringContainer
     {
         public string Text
         {

Microsoft.Toolkit.Uwp.UI/Behaviors/FocusBehavior.cs

@@ -168,7 +168,7 @@ public sealed class FocusTargetList : List<FocusTarget>
     /// <summary>
     /// A target for the <see cref="FocusBehavior"/>.
     /// </summary>
-    public sealed class FocusTarget : DependencyObject
+    public sealed partial class FocusTarget : DependencyObject
     {
         /// <summary>
         /// The DP to store the <see cref="Control"/> property value.

Microsoft.Toolkit.Uwp.UI/Converters/BoolToObjectConverter.cs

@@ -12,7 +12,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Converters
     /// This class converts a boolean value into an other object.
     /// Can be used to convert true/false to visibility, a couple of colors, couple of images, etc.
     /// </summary>
-    public class BoolToObjectConverter : DependencyObject, IValueConverter
+    public partial class BoolToObjectConverter : DependencyObject, IValueConverter
     {
         /// <summary>
         /// Identifies the <see cref="TrueValue"/> property.

Microsoft.Toolkit.Uwp.UI/Converters/DoubleToObjectConverter.cs

@@ -15,7 +15,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Converters
     /// Otherwise the logic looks for the value to be GreaterThan or LessThan the specified value.
     /// The ConverterParameter can be used to invert the logic.
     /// </summary>
-    public class DoubleToObjectConverter : DependencyObject, IValueConverter
+    public partial class DoubleToObjectConverter : DependencyObject, IValueConverter
     {
         /// <summary>
         /// Identifies the <see cref="TrueValue"/> property.

Microsoft.Toolkit.Uwp.UI/Converters/EmptyObjectToObjectConverter.cs

@@ -12,7 +12,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Converters
     /// This class converts an object value into a an object (if the value is null returns the false value).
     /// Can be used to bind a visibility, a color or an image to the value of an object.
     /// </summary>
-    public class EmptyObjectToObjectConverter : DependencyObject, IValueConverter
+    public partial class EmptyObjectToObjectConverter : DependencyObject, IValueConverter
     {
         /// <summary>
         /// Identifies the <see cref="NotEmptyValue"/> property.

Microsoft.Toolkit.Uwp.UI/Converters/TypeToObjectConverter.cs

@@ -11,7 +11,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Converters
     /// <summary>
     /// This class returns an object or another, depending on whether the type of the provided value matches another provided Type.
     /// </summary>
-    public class TypeToObjectConverter : DependencyObject, IValueConverter
+    public partial class TypeToObjectConverter : DependencyObject, IValueConverter
     {
         /// <summary>
         /// Identifies the <see cref="TrueValue"/> property.

Microsoft.Toolkit.Uwp.UI/Helpers/BindableValueHolder.cs

@@ -12,7 +12,7 @@ namespace Microsoft.Toolkit.Uwp.UI.Helpers
     /// Can be used to change several objects' properties at a time.
     /// </summary>
     [ContentProperty(Name = nameof(Value))]
-    public class BindableValueHolder : DependencyObject
+    public partial class BindableValueHolder : DependencyObject
     {
         /// <summary>
         /// Identifies the <see cref="Value"/> property.

Microsoft.Toolkit.Uwp.UI/Microsoft.Toolkit.Uwp.UI.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="MSBuild.Sdk.Extras">
 
   <PropertyGroup>
-    <TargetFramework>uap10.0.17763</TargetFramework>
+    <TargetFrameworks>uap10.0.17763</TargetFrameworks>
     <LangVersion>8.0</LangVersion>
     <Title>Windows Community Toolkit UI</Title>
     <Description>

Microsoft.Toolkit.Uwp/Microsoft.Toolkit.Uwp.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="MSBuild.Sdk.Extras">
 
   <PropertyGroup>
-    <TargetFramework>uap10.0.17763</TargetFramework>
+    <TargetFrameworks>uap10.0.17763</TargetFrameworks>
     <Title>Windows Community Toolkit</Title>
     <Description>This package includes code only helpers such as Colors conversion tool, Storage file handling, a Stream helper class, etc.</Description>
     <PackageTags>UWP Toolkit Windows</PackageTags>