Migrate dispatcher index to tsx

Summary: As per the title

Reviewed By: jknoxville, passy

Differential Revision: D16690303

fbshipit-source-id: fa78ea1e3f288249676d5a6423e5d0f0a6e427a4

src/dispatcher/types.tsx

@@ -10,4 +10,4 @@ import {Logger} from '../fb-interfaces/Logger';
 export type Dispatcher = (
   store: Store,
   logger: Logger,
-) => (() => Promise<void>) | null;
+) => (() => Promise<void>) | null | void;