Replace onTaskMovedToFront with a transition observer in bubbles

The TaskStackListenerCallback is not synchronized with shell transit
which results in this bug. Instead of using it, use a Transition
Observer to see when tasks are opening / moving to front.

To ensure home / recents are handled correctly (since we don't
get shell transitions for those), start checking for recentapps
and homekey in the close system dialogs broadcast.

Test: atest PlatformScenarioTests:android.platform.test.scenario.sysui.bubble.ShowBubbleAndShowImeTest#testShowBubbleAndShowIme
Test: atest BubblesTransitionObserverTest BubblesTest
Test: - have more than 1 bubble and have a telegram bubble
      - hit the 'x' in telegram UI to finish the activity
      => observe that the next bubble is selected
Bug: 296821517
Change-Id: I60fe7b619d2433c5ed1e085cee7c3d564d77cd92