Introduce BubbleBarLayerView & animation for BubbleBarExpandedView

* BubbleBarLayerView will be used in place of BubbleStackView when the
  bubbles are shown in the bubble bar in launcher. It'll be added to
  the window manager instead and it'll host and animate the expanded
  view for bubbles from the bubble bar.

* BubbleBarExpandedViewAnimationHelper contains code to animate the
  expanded view shown in BubbleBarLayerView.

* This CL just adds the classes, usuage of them happens in a future
  CL.

Test: treehugger / manual with other CLs
Bug: 253318833
Change-Id: I79ab3cbe357439f1ec51d48c5f06504b899509f0