Initial animation of new bubble bar bubble

This change animates a new bubble bar bubble. Currently only handles the case where the bubble is added when the bubble bar is stashed.
There's no synchronization with the stash handle yet either.

Flag: ACONFIG com.android.wm.shell.enable_bubble_bar DEVELOPMENT
Bug: 280605790
Test: atest BubbleBarViewAnimatorTest
Change-Id: Ic3f5edc0dde204f871cf7e1288bd50620e6beebb