Animate new bubble when the bar is expanded

When a new bubble is added when the bubble bar is expanded,
we now scale in the new bubble.

This change only handles the case where we're not at the limit.

Demo: http://recall/-/bJtug1HhvXkkeA4MQvIaiP/hW4pwqpAttscedRMxnu5BN

Flag: com.android.wm.shell.enable_bubble_bar
Bug: 345795791
Test: manual
      - Expand bubble bar
      - Push a new bubble and verify it scales in
Change-Id: Iafae1d0c8feb8e5a8853d54e7299db261df4ebf4