Summary:
Resolves#13012
RCTPushNotificationManager uses startObserving to register for RCTRegisterUserNotificationSettings. According to the docs, the startObserving method won't be called until somebody subscribes to NotificationManagerIOS.
This means there is a scenario when the developer can call requestPermissions without subscribing to notifications first, but since RCTPushNotificationManager relies on NSNotificationCenter subscribtion, the result will never be returned.
When requesting permissions the promise will resolve:
`PushNotificationIOS.requestPermissions().then(console.log);` without the need for calling `PushNotificationIOS.addEventListener()` first.
Closes https://github.com/facebook/react-native/pull/13263
Differential Revision: D4851767
Pulled By: javache
fbshipit-source-id: 2be8621e072ae1086014594bc986ca5590b5eb61
d03f9b7442