Add NSSL alpha support for DREAMING<->LOCKSCREEN

The notifications didn't fade properly coming in and out of
dreaming. And due to delays in processing the legacy occlusion
pipeline, add 100ms of time to the transition.

Also, refactor the nested flatmaps into a more sane structure.

Also, make sure notification fades as QS expands

Fixes: 322156469
Fixes: 322198225
Test: foldables/tablets, enter in and out of dreaming in search of any
lockscreen content flicker
Flag: ACONFIG com.android.systemui.keyguard_shade_migration_nssl
DEVELOPMENT

Change-Id: Id54ee363c32f6ec3a38c25bf7b606b5a12cde205