Remove non-null assertion in ConversationProvider

- Add `createOptionalContext` that is used by `AuthContext` and `ConversationContext` to create a context with a hook
  that can be used to retrieve its value and throw an error if it's undefined.
- In `router.tsx`, put `Messenger` inside `ConversationProvider`.
- In `ConversationListItem`, use the conversationId from the `ConversationContext ` instead of the url params.
- Fix bug in `CallInterface` with fullscreen.
- Remove unecessary useEffect dependency in `NotificationManager`.

Change-Id: Ib5f0ae6a0a34cdbdb02f871e36194376d945230d
diff --git a/client/src/contexts/WebRtcProvider.tsx b/client/src/contexts/WebRtcProvider.tsx
index 4cd6263..59999b9 100644
--- a/client/src/contexts/WebRtcProvider.tsx
+++ b/client/src/contexts/WebRtcProvider.tsx
@@ -22,7 +22,7 @@
 import LoadingPage from '../components/Loading';
 import { WithChildren } from '../utils/utils';
 import { useAuthContext } from './AuthProvider';
-import { ConversationContext } from './ConversationProvider';
+import { useConversationContext } from './ConversationProvider';
 import { IWebSocketContext, WebSocketContext } from './WebSocketProvider';
 
 export type MediaDevicesInfo = Record<MediaDeviceKind, MediaDeviceInfo[]>;
@@ -99,7 +99,7 @@
   webRtcConnection: RTCPeerConnection;
   webSocket: IWebSocketContext;
 }) => {
-  const { conversation, conversationId } = useContext(ConversationContext);
+  const { conversation, conversationId } = useConversationContext();
   const [localStream, setLocalStream] = useState<MediaStream>();
   const [remoteStreams, setRemoteStreams] = useState<readonly MediaStream[]>();
   const [iceConnectionState, setIceConnectionState] = useState<RTCIceConnectionState | undefined>();