export types from messaging exp (#4353)

Author: Feiyang1

packages-exp/messaging-exp/src/index.ts

@@ -19,7 +19,14 @@ import { FirebaseMessaging } from '@firebase/messaging-types-exp';
 import { registerMessaging } from './helpers/register';
 import '@firebase/installations-exp';
 
-export { getToken, deleteToken, onMessage, getMessaging } from './api';
+export {
+  getToken,
+  deleteToken,
+  onMessage,
+  getMessaging,
+  FirebaseMessaging,
+  MessagePayload
+} from './api';
 
 declare module '@firebase/component' {
   interface NameServiceMapping {