[CommRustModule] add JSI bindings for findUserIdentities RPC
Summary:
This diff exposes FindUserIdentities to JavaScript
Depends on D11998
Test Plan: Tested later in stack by calling rpc on web/native
Reviewers: kamil, bartek
Reviewed By: bartek
Subscribers: ashoat, tomek
Differential Revision: https://phab.comm.dev/D11999