Implement UMO transitions to & from the communal hub

Bug: 311243906
Fix: 311243906
Test: verified UMO transitions to & from keyguard and dream
Test: atest MediaHierarchyManagerTest
Flag: ACONFIG com.android.systemui.communal_hub STAGING
Change-Id: Iaaba3e3d2d83815082e940d7741375e5f6e01329
10 files changed