[Bubbles] Fix flicker when collasping and expanding bubble

The bubble TaskView is removed after collasping, and it is added
back when expanded. However, if this happens quickly, the expand
animation may have a flicker due to TaskView visibility. This CL
avoids the removal of the TaskView if expand animation starts
before the completion of collasp animation by adding reference
counting of animating bubbles.

Bug: 403612574
Test: atest BubbleBarLayerViewTest; Manual
Flag: EXEMPT bugfix
Change-Id: I1891f8ad312b2dbc550a39abc7d6e878e46354de