feat: Allow stopping composition animation

[zxbmmmmmmmmm]

What does the pull request do?

This pull request introduces StopAnimation(propName) to the CompositionObject class to allow stopping animations on a specific property and StopAnimationGroup(grp) to stop an animation group. This addition improves the control developers have over property animations in the composition system.

What is the current behavior?

Currently, to stop a composition animation, we can only start another animation on the same property.

What is the updated/expected behavior with this PR?

Now we can use StopAnimation(propName) or StopAnimationGroup(grp) to stop animations on CompositionObject

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with user documentation

Breaking changes

None

Obsoletions / Deprecations

None

[avaloniaui-bot]

You can test this PR using the following package version. 12.0.999-cibuild0060060-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[avaloniaui-bot]

You can test this PR using the following package version. 12.0.999-cibuild0060062-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]