Introduce CommIOSNotifications class in JavaScript

Summary:
This differential introduces CommIOSNotification class to JavaScript. It is equivalent of IOSNotification class from previously used Ashoat's fork. We need this class since it parses structure of raw Apple notification into more meaningful JavaScript object we rely on in various callbacks in
push-handler.

Test Plan: Flow and Eslint do not complain. Very next differential will use this class in JavaScript callbacks to various events send from native code.

Reviewers: tomek, atul, ashoat

Reviewed By: tomek, ashoat

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D6138