Removed IInternalImplicitAnimation, moved event to public interface

See #3843 (comment)

Author: Sergio0694

Microsoft.Toolkit.Uwp.UI.Animations/Xaml/Abstract/ImplicitAnimation{TValue,TKeyFrame}.cs

@@ -15,11 +15,11 @@ namespace Microsoft.Toolkit.Uwp.UI.Animations
     /// A base model representing a typed animation that can be used as an implicit composition animation.
     /// </summary>
     /// <inheritdoc cref="Animation{TValue, TKeyFrame}"/>
-    public abstract class ImplicitAnimation<TValue, TKeyFrame> : Animation<TValue, TKeyFrame>, IImplicitTimeline, IInternalImplicitAnimation
+    public abstract class ImplicitAnimation<TValue, TKeyFrame> : Animation<TValue, TKeyFrame>, IImplicitTimeline
         where TKeyFrame : unmanaged
     {
-        /// <inheritdoc cref="IInternalImplicitAnimation.AnimationPropertyChanged"/>
-        private event EventHandler? AnimationPropertyChanged;
+        /// <inheritdoc/>
+        public event EventHandler? AnimationPropertyChanged;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="ImplicitAnimation{TValue, TKeyFrame}"/> class.
@@ -37,13 +37,6 @@ protected ImplicitAnimation()
             RegisterPropertyChangedCallback(KeyFramesProperty, RaiseAnimationPropertyChanged);
         }
 
-        /// <inheritdoc/>
-        event EventHandler? IInternalImplicitAnimation.AnimationPropertyChanged
-        {
-            add => AnimationPropertyChanged += value;
-            remove => AnimationPropertyChanged -= value;
-        }
-
         /// <summary>
         /// Gets or sets the optional implicit target for the animation. This can act as a trigger property for the animation.
         /// </summary>

Microsoft.Toolkit.Uwp.UI.Animations/Xaml/ImplicitAnimationSet.cs

@@ -62,7 +62,7 @@ private void ImplicitAnimationSetVectorChanged(IObservableVector<DependencyObjec
             if (@event.CollectionChange == CollectionChange.ItemInserted ||
                 @event.CollectionChange == CollectionChange.ItemChanged)
             {
-                IInternalImplicitAnimation item = (IInternalImplicitAnimation)sender[(int)@event.Index];
+                IImplicitTimeline item = (IImplicitTimeline)sender[(int)@event.Index];
 
                 item.AnimationPropertyChanged -= RaiseAnimationsChanged;
                 item.AnimationPropertyChanged += RaiseAnimationsChanged;

Microsoft.Toolkit.Uwp.UI.Animations/Xaml/Interfaces/IImplicitTimeline.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using Windows.UI.Composition;
 using Windows.UI.Xaml;
 
@@ -14,6 +15,13 @@ namespace Microsoft.Toolkit.Uwp.UI.Animations
     /// </summary>
     public interface IImplicitTimeline
     {
+        /// <summary>
+        /// Raised whenever a property that influences the animation changes.
+        /// This event is used by <see cref="ImplicitAnimationSet"/> to update the animations collection
+        /// assigned to a target <see cref="UIElement"/> when any of the individual animations is modified.
+        /// </summary>
+        event EventHandler? AnimationPropertyChanged;
+
         /// <summary>
         /// Gets a <see cref="CompositionAnimation"/> from the current node. This animation might
         /// be used either as an implicit show/hide animation, or as a direct implicit animation.