[native] Move QR and sign-in files around

Summary:
Move the QR-related utils to the utils directory and sign-in related files to the account directory.

Depends on D14051

Test Plan: Flow. Tested in combination with the rest of the stack.

Reviewers: kamil, angelika, bartek

Reviewed By: kamil

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D14052