Notify app clients about managed Bubbles removals

The user can remove a Bubble requested by an app. This adds
a callback to notify the app, so that it can clean up its internal
state and avoid requestiong actions on a Bubble that's no longer
there.

IMultitaskingControllerCallback is used by Shell to notify the
MultitaskingController in WM Core, which will then pass it to
BubbleContainerManager in the client process.

The BubbleContainerCallback is the public extensions API used to
notify the application.

MultitaskingController also automatically cleans up the bubbles if
the client process dies.

Bug: 407149510
Flag: com.android.window.flags.enable_experimental_bubbles_controller
Test: Manual, removing a Bubble created by the demo app
Change-Id: I52e2196dcdd7ee3896d5298260bb1979943aa04f