Hide both pausing and closing tasks when finishing the recents transition

- If we try to merge a transition that closes a pausing task, the task
  will be removed from the pausing set, but not actually handled during
  cleanup and may result in the task being visible momentarily between
  reparenting of the task out of the transition leash (applied in the
  shell) and WM committing the visibility of the task
- When handling a task view transition for a task that going TO_BACK,
  also update the surface visibility if the pending transition is also
  TO_BACK since that is only created when the taskview container's
  surface is destroyed.

Fixes: 310567149
Test: Repro on the bug
Change-Id: I1ba72a2f1b2bcd2b56f55d4c288e86ebf3e53d8c