[web][native] extract QR code login functions to separate files

Summary:
ENG-8385.

QR code login is not working right now. As described here (Point 3) and here the issue is, because of the fact that useQRAuth is unmounting before it can send SECONDARY_DEVICE_REGISTRATION_SUCCESS. This stack is refactoring the code to move logic to context (see here).

This diff purpose is to move some functions to separate places to later pass it as props to a context.

Depends on D12440

Test Plan: Flow

Reviewers: bartek, ashoat

Reviewed By: bartek, ashoat

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12445