Log when bubble bar is expanded or collapsed

Send an event when bubble bar is expanded from launcher or a new auto
expanding bubble is received.
Send an event when bubble bar is collapsed.

Bug: 349845968
Test: atest BubblesTest
Test: expand and collapse bubble bar from launcher, check event logging
Test: trigger auto-expanding bubble, check event logging
Test: switch between bubbles and drag expanded view around, check no
  expand or collapse events are logged

Flag: com.android.wm.shell.enable_bubble_bar
Change-Id: Iab5c54ac3171b9b7f3afb3e85ba839055d9e382a