Remove a task from bubbles when it is moving to split

Initial change got tagged as a perf regression: ag/33580600

Adding a bugfix flag for the initial change and also including an
improvement to filter the changes processed from: ag/33652568

Bug: 396315875
Test: atest WMShellUnitTests:BubblesTransitionObserverTest
Test: launch Calculator in a bubble, move back to home screen, start
  split screen from Messages app, choose Calculator as the second app,
  confirm that Messages and Calculator are both in split screen
Flag: com.android.wm.shell.enable_enter_split_remove_bubble
Change-Id: I43cc0983a99ca89aef32c06aab67782ea9af8a59