Change LocalMediaRepository coroutine scope to be local to the flow

chain in MediaOutputInteractor

Now coroutine scope inside LocalMediaRepository gets properly cancelled
and collected when the package name changes. Before the fix idle
coroutines were left in the application coroutine scope.

Flag: com.android.systemui.new_volume_panel
Bug: 329561499
Test: manual on the phone with a cast device and headphones
Test: atest MediaOutputInteractorTest
Change-Id: I380a968f18cdcf27793b52f772a11bf0103068ab