[native] Expose backup ct1 and ct2 functions to JS

Summary:
In addition to restoreBackup(), exposed functions that separately get backup keys and data via JSI. They're needed for secondary device auth

Depends on D11344

Test Plan: Modified backupRestoreProtocol in useClientBackup to call retrieveBackupKeys and then restoreBackupData, instead of single restoreBackup() call.

Reviewers: michal, kamil

Reviewed By: michal

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11345