Add AuthenticationService and RegistrationWizard.

[pixlwave]

This PR extracts just the service, wizard and related models from #6048 for 2 smaller PR reviews.

The Changelog will come as part of that PR.

The implementation is based on Element Android, adapting MX responses from the SDK into matching models and using async/await to mirror Kotlin's suspending functions.

Depends on matrix-org/matrix-ios-sdk#1443

[github-actions]

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[Anderas]

I am looking at the associated future PR, but unless I missed it I cannot see any tests (whether unit or integration) for a lot of this new code (only ViewModels etc). Given the amount of state changes and logic contained in this code I think it would be valuable to create them where appropriate.

The class is also quite large and managing the flow of both the registration and login, which are actually flows mutually exclusive of each other. I think it might be worth breaking this down even further for better readability, testability and to prevent this from growing unmanagabley in the future.

[pixlwave]

Moving this reply from above as it landed on the wrong comment:

I've added some basic tests for against the service for now. Currently integration but would like to mock the HTTP/REST clients once I've finished the registration flow. Will add tests for the RegistrationWizard at this point too.

[Anderas]

Thanks for addressing all the comments. I realise that a lot of the flow is still a WIP so happy to unblock this PR, and refine any remaining bits in the upcoming ones.

[pixlwave]

Thanks, sounds like a plan to me 🙌