Create a virtual default audio output

Managing your audio output manually is kind of cumbersome; Chrome creates a default audio output for us, but now that audio outputs are enabled on Firefox as well, I find it necessary for a good user experience that there always be a way to set it to "whatever the default is".

src/room/MuteStates.ts

@@ -54,12 +54,12 @@ function useMuteState(
 ): MuteState {
   const [enabled, setEnabled] = useReactiveState<boolean | undefined>(
     (prev) =>
-      device.available.length > 0 ? (prev ?? enabledByDefault()) : undefined,
+      device.available.size > 0 ? (prev ?? enabledByDefault()) : undefined,
     [device],
   );
   return useMemo(
     () =>
-      device.available.length === 0
+      device.available.size === 0
         ? deviceUnavailable
         : {
             enabled: enabled ?? false,