Save and later cancel ViewPropertyAnimator on bubble view tag

When a bubble autoexpands (via button button)
 1) order changes and reorder animations start
 2) active controller changes from StackAnimationController to ExpandedAnimationController
 3) the stack expands
 4) PhysicalAnimationLayout doesn't find reorder animations by tag, so they don't get canceled
 5) the "swoop up" reorder animation runs right after expansion completes

This change saves StackAnimationController's reorder animators on bubble
view so that PhysicsAnimationLayout cancels it when the active
controller changes to ExpandedAnimationController.

Fixes: 171850447
Bug: 170267512
Test: manual
 1) Unbubble notif
 2) Send another bubbling notif => HUN shows
 3) Tap HUN's bubble button
     => See that bubble autoexpands without leftover reorder animation
Change-Id: Idd0543659a65fddba4b4fc5bee0ff7b9aad8b352