Allow UMO to show over the dream

When dreaming, the shade can be pulled down from the top of the screen
and the UMO should appear there. In MediaHierarcyManager, this case is
handled by the condition of:
(qsExpansion > 0.0f || inSplitShade) && !onLockscreen
Since Tangor uses split shade, this condition will be true when
dreaming.

The glanceable hub can be opened from on top of the dream, so in order
to allow the UMO to show up there, we change the logic so the hub has a
higher priority, as long as the shade is closed.

Bug: 322549132
Fixed: 322549132
Test: atest MediaHierarchyManagerTest
Flag: ACONFIG com.android.systemui.communal_hub STAGING
Change-Id: I01098d16cdf8fe9f511c18aed95b411d2ba6f969