Fixes two bright flashes of the notification scrim

We were previously going to UNLOCKED state if if there was no camera
preview leading to a bright flash in light mode. we now only do this
when the whole screen is obscured anyway by the camera preview.
This also fixes another scrim issue where the unocclusion would
flash the notification scrim, because it's expanding, which
usually shows the bouncer with a bright background during the
expansion.

Test: atest SystemUITests
Fixes: 197160246
Merged-In: I418e878698c2606856b93faf774cd87830773815
Change-Id: I418e878698c2606856b93faf774cd87830773815