Only skip stacks behind home when not in multi-window mode.

Split screen primary stack is behind home (though visible to user), and
needs to respond to user tapping when out of touch region.

This doesn't cover the case where split screen stacks and freeform
stacks both exist in the display, but that's not a very common case on
any form factor.

Bug: 117777954
Bug: 117824834
Test: IME is brought up when Gmail is in split screen primary stack.
Tapping on home won't focus on home stack.
atest android.autofillservice.cts.MultiWindowLoginActivityTest#testSplitWindow

Change-Id: I44e17d9a0eba3ab6669ef75223c982ae0e811fc6