Fix fallback recents not updating list from app

When launching an from recents, onStop is not called until the app is
fully taken over and the remote animation finishes. As a result, if the
user hits the overview button right before the animation finishes, we
animate back to recents but never call onStart which is where we hook in
to update the recents list.

The fix naturally is to move this to onResume instead as once the
animation begins, the activity is paused.

Bug: 132293341
Test: Repro from bug, correctly updates
Change-Id: Ie6cfdc4d5aa6b1742a3bce3e14ab5ab6a4f05526