Connect carousel UI to pipeline

This CL includes some fixes in media control view-model and media
carousel interactor. These fixes were essential in running the code
without any crashes.

Flag: ACONFIG com.android.systemui.media_controls_refactor DISABLED
Bug: 328207006
Test: atest SystemUiRoboTests:MediaControlViewModelTest
Test: atest MediaCarouselControllerTest
Test: Build.
Test: Checked UI with flexiglass turned on/off, with refactor flag
turned off/on.

Change-Id: Iff63792d5c0c8563cce696fd62cf72a54d0d47f7