[Flexiglass] Hide carousel based on lock screen setting

If the user has opted to hide media on the lockscreen, do not generate a
MediaCarousel when the device is locked

Fixes: 360131963
Flag: com.android.systemui.scene_container
Test: manual
Test: MediaCarouselControllerTest
Change-Id: I66cc8293598a303ea901eb0cfea5eccc7d0e3524