Return to correct home stack task in multi-window mode

Previously when determining the next stack to focus to in
multi-window mode, if it is the home stack we just bring it
forward and focus on whatever the home task/activity is.
We should be checking the returnToTask type of the activity/task
that is going away to determine which task in the home stack
we should return to.

Bug: 27776008
Change-Id: I1a864c96b2ef276d2ddeafcb627a2b6a825e2ce7