Log when bubble is moved to overflow

Log when there are too many bubbles in the bubble bar and the oldest
bubble gets moved to overflow.

Bug: 349845968
Test: atest com.android.wm.shell.bubbles.BubbleDataTest
Test: manual, trigger multiple bubbles until there are too many, check
  that when oldest bubble moves to overflow, event is logged
Flag: com.android.wm.shell.enable_bubble_bar
Change-Id: Ib6f2f9a48772c0571291c80ab301b2ddc9b95c00