AudioDetailsView: Store current input device in MediaSwitchingController

Add an instance to manage current input device, and also add
MediaSwitchingControllerExt to add a flow, that will be used to display
current input device in the audio details view.

Bug: 442004274
Test: manual
Flag: com.android.systemui.qs_tile_detailed_view
Change-Id: I8b1725701457f7a9143cbdc8f1a90ee00a4c097b