Add transitions between glanceable hub and occluded state

Glanceable hub may be occluded when launching a showWhenLocked activity
from a widget on the hub or when dreaming starts/stops. This change
only ensures KeyguardState is accurate, it doesn't include any of the
animation work that may be needed.

Bug: 319719842
Flag: ACONFIG com.android.systemui.communal_hub DEVELOPMENT
Test: atest KeyguardTransitionScenariosTest
Change-Id: I4ddf547aa1517fbc7ec5f7f993d5da0a814d5b1c