This CL allows disassociating the leaf task if relaunched and
reparented it to TDA as root task for split-screen.
Bug: 236317871
Test: atest WindowOrganizerTests
Change-Id: I6704fab733ed7d239d7004c93d3d2f471ac94822
Merged-In: I6704fab733ed7d239d7004c93d3d2f471ac94822