Convert overflow floating bubble from task

Implements the methods in BubbleStackView for supporting a bubble
transition from an existing task. The behavior is currently
restricted to converting tasks to bubbles that exist in overflow.

Fixes: 407475117
Flag: com.android.wm.shell.enable_create_any_bubble
Test: manual
       - create a floating bubble
       - long press on an app and bubble it
       - dismiss the app bubble to move it to overflow
       - launch the same app to full screen
       - expand bubbles
       - switch to overflow and promote the app bubble
       - verify the full screen task converted to bubble
Change-Id: Iae2a9eeff471d5db535493b2539d223c588ea052