[native] login wallet user (C++)

Summary:
call the new rust client method from C++

Depends on D7809

Test Plan: was able to successfully call the identity service RPC from JS. this will be tested more rigorously when we actually change the login callsites on native

Reviewers: ashoat

Reviewed By: ashoat

Subscribers: tomek, atul

Differential Revision: https://phab.comm.dev/D7810