Fix task-organizer + shell transit interractions during tests

During tests, task-organizers sometimes get registered/unregistered
overtop the shell task-organizer. This can race with transition
animations (most common during teardown where the instrumentation
isn't waiting for anything and doesn't know what the test was
doing).

To remedy this, add a waiting mechanism to transition controller so
that these operations (like register/unregister) won't run during
transition animations. This is designed to have basically 0 impact
on normal usage.

Also, because chanhing organizers goes through a "migrateSurface"
flow, it can also mix-up unfavorably with transitions (esp. in cases
where Shell uses transitions to handle visibility). For this one
case, we manually "show" task surfaces after they've been migrated
even for organized tasks. This simulates the desired effect that
register/unregister shouldn't alter the system state.

Bug: 183993924
Test: atest CrossAppDragAndDropTests
Change-Id: I6a8f80fe92442e1ac12be8e5ff4322b58567157a