Invoke AnimationFinished from fragment if no animation has been added

[PureWeen]

Description of Change

ShellItemRenederer on Android let's users override SetupAnimation to define custom animations. The navigation code on android subscribes to "AnimationFinished" to know when the animation has finished and complete the navigation Task. The problem here is that if the SetupAnimation doesn't actually setup an animation then "AnimationFinished" never gets called from ShellContentFragment. The real fix here will be to add a better API for the SetupAnimation override. Currently it's just

SetupAnimation(ShellNavigationSource navSource, AndroidX.Fragment.App.FragmentTransaction t, Page page)

But it should really be something like

SetupAnimation(ShellNavigationSource navSource, AndroidX.Fragment.App.FragmentTransaction t, Page page, Action callMeWhenAnimationHasFinished)

Or something similar to indicate to the caller that they need to tell the calling code when the animation has completed.

Platforms Affected

• Android

Testing Procedure

• UI Test Included

PR Checklist

• Targets the correct branch
• Tests are passing (or failures are unrelated)

[PureWeen]

Basically if the user creates a custom renderer that doesn't actually add an animation then the following code

https://github.com/xamarin/Xamarin.Forms/blob/5.0.0/Xamarin.Forms.Platform.Android/Renderers/ShellItemRendererBase.cs#L254

will never execute and the "async push" operation will never complete

This invokes the AnimationFinished event so the calling code can continue on and complete the animation Task

[rmarinho]

Failing tests not related