Extract AnimateContent out of AnimateToScene

This CL is a pure refactoring that extracts some utility methods to
animate content using one-off transitions. This will be used to animate
overlays that are enabled/disabled.

Bug: 353679003
Test: atest PlatformComposeSceneTransitionLayoutTests
Flag: com.android.systemui.scene_container
Change-Id: Ieb1bcc679e2c26f3d0dd569fa90e6e0d10aa8f1f