Fix multiple issues with device settings

To track media devices, we were previously relying on a combination of LiveKit's useMediaDeviceSelect hook, and an object called UserChoices. Device settings should be accessible from outside a call, but the latter hook should only be used with a room or set of preview tracks, so it couldn't be raised to the app's top level. I also felt that the UserChoices code was hard to follow due to lack of clear ownership of the object.

To bring clarity to media device handling and allow device settings to be shown outside a call, I refactored these things into a single MediaDevicesContext which is instantiated at the top level of the app. Then, I had to manually sync LiveKit's device state with whatever is present in the context. This refactoring ended up fixing a couple other bugs with device handling along the way.

src/settings/useSetting.ts

@@ -115,9 +115,9 @@ export const useDeveloperSettingsTab = () =>
 export const useShowConnectionStats = () =>
   useSetting("show-connection-stats", false);
 
-export const useDefaultDevices = () =>
-  useSetting("defaultDevices", {
-    audioinput: "",
-    videoinput: "",
-    audiooutput: "",
-  });
+export const useAudioInput = () =>
+  useSetting<string | undefined>("audio-input", undefined);
+export const useAudioOutput = () =>
+  useSetting<string | undefined>("audio-output", undefined);
+export const useVideoInput = () =>
+  useSetting<string | undefined>("video-input", undefined);