Allow non-doze dreams to be windowless

Support wallpaper dream to be windowless and use
keyguard as the view. Transitions look alike AOD.
Add the logic to stop dreaming after unlocking
via bouncer.
Allow SystemUI dreams to be windowless.

Bug: b/285059232
Test: atest KeyguardViewMediatorTest; on device
Change-Id: I3348a7d9c8c437c87a8049d879209e620c80771d