[lib/web/native] rename toggle pin utils to be message pinning utils

Summary:
Simple rename diff. Plan to introduce other message pinning utils in this file and figured I would make the file name a bit more general

Depends on D10345

Test Plan: flow

Reviewers: atul, rohan, kamil

Reviewed By: rohan

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10346