Work challenge did not show when a work activity is not on top, but
still visible after screen turns on.
Also show work challenge even if the work activity is behind a top
fullscreen activity of another profile because the user can still
navigate back to the work activity when top activity finishes.
Bug: 177457096
Test: ActivityStackSupervisorTests
Change-Id: I5e09b09be547d04fdfd709cb9cd4bcd4a94bbf21
Merged-In: I5e09b09be547d04fdfd709cb9cd4bcd4a94bbf21
6820d70823