[flexiglass] Light reveal scrim

Adds the light reveal scrim effect to Flexiglass.

Bug: 372051441
Test: manually verified that the light reveal works when going to sleep
and waking up using the power button, when unlocking from face unlock,
and when lifting up the device
Flag: com.android.systemui.scene_container

Change-Id: Id7ff0dcd4f590e1b7ef4e3b67179a44613166bc4