Update behind scrim if occlusion changes

If the scrim state is AOD or PULSING and the device is in
occluded state, the behind scrim is set to 1 to ensure the
app isn't visible underneath AOD. If the occlusion state
changes, undo that change.

Fixes: 423364430
Test: atest ScrimControllerTest
Flag: EXEMPT bugfix
Change-Id: I4bec38382ff6cb49b4326cc611adffcc6791783e