Add TaskFragmentOrganizer#onActivityReparentToTask

When the activity exits PiP and is reparented to the original Task, the
organizer should handle it as a new launch.

Bug: 225371112
Test: atest WmTests:TaskFragmentTest
Test: atest WmTests:TaskFragmentOrganizerControllerTest
Change-Id: Ia7e32e995a35e167b0d76e701c972b269ae068cc