[native] helper for pake registration on client side

Summary:
This helper function takes the registration response from the server and completes the final step on the client side. It handles the error mapping and checking if the ClientRegistration object is present

Depends on D4799

Test Plan: Tested two diffs later in the stack

Reviewers: tomek, karol

Reviewed By: tomek

Subscribers: ashoat, adrian, atul, abosh

Differential Revision: https://phab.comm.dev/D4800