[lib][native] Unshim FARCASTER_MUTUAL messages on the client

Summary:
This addresses ENG-7991 and ENG-7992.

Depends on D11871

Test Plan: Tested sending a shimmed message to a client (both native and web) and confirmed it was unshimmed

Reviewers: ginsu, atul

Reviewed By: ginsu

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D11883