Make sure tasks below home task is invisible while in split

While in split mode, home task will be reparented to the secondary split
and leaving tasks not supporting split below. Because TaskDisplayArea
always adjusts home surface layer to the bottom, this makes sure those
tasks below home is invisible and won't occlude home task unexpectedly.

Fix: 185872271
Fix: 159767867
Test: dock translucent task to split primary while having task not
supporting split in recent, recent app won't be occluded.

Change-Id: Ie110ea302a0ec646b6c39f68606b31cd4c26697e