Upgrade eslint-plugin-matrix-org to 1.2.1

This upgrade came with a number of new lints that needed to be fixed across the code base. Primarily: explicit return types on functions, and explicit visibility modifiers on class members.

src/room/useRoomAvatar.ts

@@ -19,8 +19,9 @@ import { Room } from "matrix-js-sdk/src/models/room";
 
 import { useRoomState } from "./useRoomState";
 
-export const useRoomAvatar = (room: Room) =>
-  useRoomState(
+export function useRoomAvatar(room: Room): string | null {
+  return useRoomState(
     room,
     useCallback(() => room.getMxcAvatarUrl(), [room])
   );
+}