[native] Extract device token reducer to lib

Summary: We will want to treat the device token similarly on web as on native. This diff extracts the native device token reducer to lib.

Test Plan: Check if device token is correctly saved in redux on new user login.

Reviewers: tomek, atul, ashoat

Reviewed By: ashoat

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D6885