Ensure RoomListStore2 gets reset when the client becomes invalidated

Fixes https://github.com/vector-im/riot-web/issues/14384

We also make use of the new AsyncStore type to handle this more safely.

test/components/views/rooms/RoomList-test.js

@@ -109,7 +109,7 @@ describe('RoomList', () => {
         client.getRoom = (roomId) => roomMap[roomId];
 
         // Now that everything has been set up, prepare and update the store
-        await RoomListStore.instance.makeReady(client);
+        await RoomListStore.instance.makeReady();
 
         done();
     });