[Dual Shade] Add UMO (media controls) to the notifications shade.

Fix: 395616939
Test: Manually tested by adding active media playback and observing it
 is rendered in notifications shade.
Test: Added unit tests.
Test: Existing unit tests still pass.
Flag: com.android.systemui.scene_container
Change-Id: I75b64ceb3d25d90e030260258b289f7e1570f54e