When the last activity finishes in the stack we're looking for other
stacks and making it focused. However we weren't doing that if the
stack was on a secondary display, so the focused stack records were
not updated in stack supervisor.
Now we're looking for other stacks on the same display first. If there
is nothing focusable left - shifting focus to next focusable display.
Test: android.server.cts.ActivityManagerDisplayTests
Test: #testStackFocusSwitchOnDisplayRemoved
Test: #testStackFocusSwitchOnStackEmptied
Change-Id: Ifbb893e12cbe9c4928b949a86fc8bc027de181e4
7fc22812ce