Fade to black without showing system wallpaper

When on the lock screen, and going to AOD animated, user would
temporarily see the system wallpaper. That's not what we want,
we want to fade from semi-transparent black to black, on top
of the backdrop - lock screen wallpaper or media art.

Test: press power on the lock screen when playing media
Test: press power on the lock screen after dismissing media
Test: unlock from AOD
Test: atest packages/SystemUI/tests/src/com/android/systemui/statusbar/phone/ScrimControllerTest.java
Fixes: 80575770
Change-Id: I6796e844add889ff86be0cd2052db7c5d5073039