Implement native method to update badge count and use it in JavaScript

Summary: This differential implements native method to update application badge count and uses it in JavaScript. Relevant types are adjusted as well.

Test Plan:
Build the app. Send several messages, open the app but do not read messages. Close the app and ensure that there is unread badge on app icon. Open the app, read messages and close the app.
Ensure that badge disappears from app icon.

Reviewers: tomek, bartek

Reviewed By: tomek, bartek

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D6378