Fix dismissing activity getting relaunch signal while dismissing split

When applying dismissing split window container transaction to reparent
child tasks out of split roots, it'll schedule update multi window mode
change.

Prevent sending relaunch signal to the dismissing activity which won't
be visible after split dismissed by considering visibility while
applying new configuration for multi window mode udpate.

Fix: 194646075
Test: enter split screen, drag divider bar to dismiss split, checked
      the dismissing activity won't get relaunch signal.
Change-Id: Ifb40fcbf89abaaa1bfb76e5018b31fc95778925d