Export EmitterSubscription TypeScript Type

Summary:
Discovered when bumping the RN documentation to typecheck against 0.72, facebook#36109 removed the `EmitterSubscription` type which should be kept public.

Changelog:
[General][Fixed] -  Export EmitterSubscription TypeScript Type

Differential Revision: D44375081

fbshipit-source-id: 859078b71044e8a70a25062ced5c8429a63c23be

Author: NickGerleman

packages/react-native/types/__typetests__/index.tsx

@@ -40,6 +40,7 @@ import {
   DrawerLayoutAndroid,
   DrawerSlideEvent,
   DynamicColorIOS,
+  EmitterSubscription,
   FlatList,
   FlatListProps,
   GestureResponderEvent,

packages/react-native/types/index.d.ts

@@ -147,6 +147,7 @@ export * from '../Libraries/Utilities/Platform';
 export * from '../Libraries/Vibration/Vibration';
 export * from '../Libraries/YellowBox/YellowBoxDeprecated';
 export * from '../Libraries/vendor/core/ErrorUtils';
+export {EmitterSubscription} from '../Libraries/vendor/emitter/EventEmitter';
 
 export * from './public/DeprecatedPropertiesAlias';
 export * from './public/Insets';