Fix broken Splitscreen in Overview on orientation change in foldables

We should make sure that only either `topMargin` or a Y translation is
used at a time on an Overview snapshot view to avoid seeing the snapshot
shifted down by an unexpected amount.

Detailed explanation can be found here: https://b.corp.google.com/issues/347143158#comment16

Fixes: 347143158
Test: Manually by following the steps described in the above comment and
      verifying the bug no longer repros.
Flag: EXEMPT bugfix
Change-Id: I699b0ccd9630c10d973fc28abb1228359184929b