Ensure media player shows

Need to add a getter to the isMediaVisible field so that we can read the
value in when we are recomposing.

Bug: 301968149
Test: turn on recording app and play sound and go back to LS
Flag: ACONFIG com.android.systemui.compose_lockscreen DEVELOPMENT
Change-Id: I944d065838d5cef5b3d83ba8f78f38eb4dbfacf7