Fix stale pending task view transition

LaunchNewTaskBubbleForExistingTransition enqueues an external transition in
TaskViewTransitions after the bubble is inflated. The external transition
is cleaned up after the transition starts playing. There could be cases
where the transition starts playing before the bubble finished inflating, so
we would end up enqueuing a transition and not cleaning it up.

This change moves the external transition cleanup until after the bubble
starts expanding, which requires the bubble to be inflated already.

Fix: 425726457
Flag: com.android.wm.shell.enable_create_any_bubble
Test: atest BubbleTransitionsTest
Test: manual
       - Repeatedly bubble google tv and interrupt the open animation by
         tapping outside it
Change-Id: Ic208e533350097f6e76c3bcffaade73c9c505a67