This is not a strict port of the original code as that used GtkBuilder, while this is now its own widget.
Additionally, moving to HdyPreferencesGroup means the Audio/Video sections are now vertically boxed, but that seems better as it was fairly wide before.

Opened Prefs, changed VV ones a bit to make sure it didn't break. Enabled test pipelines, then switch stacks to make sure they auto-disabled. Unplugged/plugged in a mic to check that the device list re-population did not lose the configured device.