Add & implement interface for BubbleTransitions to animate bubble views

Currently, BubbleTransitions only considers BubbleBarLayerView. This
means there are some issues in floating mode where BubbleStackView is
used. Namely, if a bubble'd task starts a new task, it won't get
converted into a bubble & bubbles that have a task trampoline in their
launch won't stay in the bubble.

This CL creates an interface for BubbleTransitions to communicate
with the expanded view parents (layerView & stackView). This is
the quickest/least invasive way to resolve these issues.

There's not a whole lot BubbleStackView needs to do for the interface as
we are not supporting fullscreen transitions right now, but that
will be something we need to handle in the future. At that point in
time, it might be worth considering extracting out a common animator
that can animate BubbleExpandedView/BubbleBarExpandedView (or even
try to have a common expanded view) and have one of those implement
this  interface instead.

Flag: com.android.wm.shell.enable_create_any_bubble
Bug: 408453889
Test: atest BubbleStackViewTest BubbletransitionsTest DefaultMixedHandlerTest
Test: manual - create a gmail bubble on phone, tap compose
             => observe that a 2nd gmail bubble is created
             => verify that both bubbles work after expand/collapse
                /switch
             - create a google tv bubble (does a task trampoline)
             => verify that google tv ends up in a bubble (note you do
                see a bit of an animation of the first task bubble added
                and then removed as well)
Change-Id: I9caf8bf68db035fd6d6ea429446ff88538030393