Add keyguard transitions between lockscreen and glanceable hub

This change tracks transitions between the lockscreen and glanceable
hub based on the hub's exposed transition state. The hub's
transitions are the source of truth for directly controlling the
keyguard transition.

UI animations and more transitions will be in future CLs.

Bug: 315205222
Test: atest CommunalInteractorTest KeyguardTransitionScenariosTest
Flag: ACONFIG com.android.systemui.communal_hub DEVELOPMENT
Change-Id: I3328b2d238cacc2ee7b2738e05ebd72e5086acac