Enable launching new tasks from a bubbled task into another bubbled task

- Intercept launches in the default mixed handler from app bubble tasks
  and notify bubbles to create a new bubble and animate the task
  accordingly
- Note: this currently does not play the convert transition since there
  is an issue with a missing snapshot for that change.  It just falls
  back to the launch animation in such cases.

Bug: 396313972
Bug: 408328557
Bug: 388651207
Flag: EXEMPT bugfix
Test: atest WMShellUnitTests
Test: Launch an app into a bubble, launch another task from that task
Change-Id: I1d0a86d87a06845442bdf254ddbf9952c47fa1bb