Port VV preferences from GtkComboBox to AdwComboRow

This removes another `GtkComboBox` and fixes the requested width of the row, so the label no longers gets squashed when you have a long device name.

Testing Done:
Opened Prefs, selected a different Audio Input, and confirmed it was saved/restored when re-opening.
Ran Test Audio and confirmed input was coming from the right input.
Disconnected an audio device and confirmed that the list re-populated correctly.
Disconnected the *selected* audio device and confirmed that the selection dropped back to Default.
Ran Test Audio, disconnected the selected audio device and confirmed the audio pipeline switched to Default device.

Reviewed at https://reviews.imfreedom.org/r/2398/