[flexiglass] Fixes occlusion (once and for all!!1)

WindowManagerLockscreenVisibilityInteractor wasn't reporting lockscreen
visibility properly to its downstream consumers. It wasn't taking
overlays into account and was pretending like the keyguard should be
reported as false when transitioning away from non-keyguard scenes
(without taking into account what scene it was transitioning _to_).

This bug, combined with the fact that if the scene container becomes
invisible (like it does due to occlusion) when turning off the display
while on a "show over lockscreen" activity like that of the Calculator
app, but doesn't seem to finish the Gone -> Lockscreen transition,
caused the downstream system to fail to report to WM that the keyguard
has become visible which is causing the attached CTS tests to fail.

Bug: 416718983
Bug: 416718898
Test: manually verified that logcat shows that ATMS is being properly
told that the keyguard has become visible when turning off the display
from the power button while the Calculator app is in the foreground
Flag: com.android.systemui.scene_container

Change-Id: Iae22946d733e08905dbf3d65298d57a178727a47