[New pipeline] Fix visibility issues

This CL has fixes for UMO visibility when scrolling and reorder issues
when having two or more UMOs in the carousel

Flag: com.android.systemui.media_controls_refactor
Bug: 340862192
Test: atest SystemUiRoboTests:MediaCarouselViewModelTest
Change-Id: I9d3aa1d40d98f11183e52f951ea1e7eb998abda9