Log when bubble bar bubble is selected

Bug: 349845968
Test: atest BubblesTest
Test: have two bubbles in bar, expand bar, check that expand event is
  logged, select other bubbles, check that switch event is logged
Test: have two bubbles, expand bar, drag selected bubble expanded view
  to dismiss, check that switch event is logged when other bubble is
  selected
Test: have two bubbles, expand bar, drag selected bubble from bar to
  dismiss, check that switch event is logged when other bubble is
  selected

Flag: com.android.wm.shell.enable_bubble_bar
Change-Id: I797fd070a6f437d837b47a21ad8f5a82a842878c