[lib][native] Introduce isLoggedInToIdentityAndAuthoritativeKeyserver

Summary:
Follow-up to the previous diff that combines isLoggedIn. This lets us factor out some logic in the codebase.

Depends on D12696

Test Plan:
This should be a simple no-op refactor, so my testing was limited:

1. Flow
2. Careful inspection of the code
3. The changes to NavigationHandler were tested as part of the stack

Reviewers: tomek, inka

Reviewed By: tomek

Differential Revision: https://phab.comm.dev/D12697