[web] update QR login flow to use QRAuthContext

Summary:
ENG-8385.

QR code login is not working right now. As described here (Point 3) and here the issue is occuring 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).

Rendering context and de-duplicating logic.

Depends on D12449

Test Plan: Test QR login flow on web. Adding a bunch of logs to make sure it works and all messages are sent.

Reviewers: bartek, ashoat

Reviewed By: bartek, ashoat

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12450