Update UMO visibility each time ongoing content is updated

If media is started while the hub is already showing, UMO visibility may
not update correctly and therefore the UMO will not show until the next
time the hub is opened. This change ensures we update the visibility
each time new ongoing content arrives.

This change also immediately snaps to the new UMO to workaround a bug in
the animateScrollToItem function.

Bug: 362304980
Test: atest CommunalViewModelTest
Test: atest CommunalInteractorTest
Flag: com.android.systemui.communal_hub
Change-Id: I1019a42af22a1c398fe5698e7deb2ebb486ec3ee