[lib] Introduce useFCNames and call it from useResolvedEntityText

Summary:
This lets us resolve Farcaster usernames in EntityText using a hook within a React component.

Depends on D11879

Test Plan: I tested resolution of Farcaster usernames in robotext. I tested iOS, Android, and web. I tested from both the sender and recipient's perspective

Reviewers: ginsu

Reviewed By: ginsu

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D11880