Workaround for apps to stop before removing the task

- With live tile enabled, the race between destroying the task and
  killing the process is more evident since the app may not get
  stopped at all.  For now, when dismissing, defer removing the
  task until we've finished the recents animation to allow the
  app to be stopped accordingly

Bug: 184899234
Test: Dismiss the task from overview, check that the app gets
      lifecycle events
Change-Id: Ib3ea479643d65859fe4cd580b4c347b87130a69d
Merged-In: Ib3ea479643d65859fe4cd580b4c347b87130a69d