Enable light templating in InAppNotification

[vgromfeld]

Adjusting some style properties of InAppNotification like the margin between the dismiss button and the content requires a full retemplate. We can avoid this by using named resources and allow a "light" templating by adjusting only the resources we want.

PR Type

What kind of change does this PR introduce?

• Feature

What is the current behavior?

The default style of InAppNotification contains fixed values that are not easily customizable like the margin for the dismiss button:

<Button x:Name="PART_DismissButton"
    Margin="24,0,0,0" />

What is the new behavior?

InAppNotification default style will now use named resources for some key layout properties.
This will allow us to only redefine those property to adjust the layout instead of going through a full retemplate.

<Button x:Name="PART_DismissButton"
    Margin="{StaticResource SystemControlMSEdgeNotificationDismissButtonMargin}">

We will now be able to customize the following properties:

<x:Double x:Key="SystemControlMSEdgeNotificationDismissButtonSize">40</x:Double>
<Thickness x:Key="SystemControlMSEdgeNotificationDismissButtonMargin">24,0,0,0</Thickness>
<x:Double x:Key="SystemControlMSEdgeNotificationDismissButtonTranslate">18</x:Double>
<VerticalAlignment x:Key="SystemControlMSEdgeNotificationDismissButtonVerticalAlignment">Center</VerticalAlignment>

PR Checklist

Please check if your PR fulfills the following requirements:

• Tested code with current supported SDKs
• Pull Request has been submitted to the documentation repository instructions. 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
• 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)
• Contains NO breaking changes

[ghost]

Thanks vgromfeld for opening a Pull Request! The reviewers will test the PR and highlight if there is any conflict or changes required. If the PR is approved we will proceed to merge the pull request 🙌

[jbrianceau]

Looks good to me 👍. I've just one suggestion that I left in a comment.

[Kyaa-dost]

Looks good 🚀

[michael-hawker]

@vgromfeld can you resolve the merge conflict here? Be careful too as #3375 also has conflicts, so not sure if incompatible.