Add support for account deactivation over SSO.

[pixlwave]

Account deactivation currently only works if the account was logged in using a password. This PR adds an AccountDeactivationService that handles the user interactive authentication using UserInteractiveAuthenticationService so that SSO (in particular SIWA) can be used to deactivate an account. Fixes #4685

One annoying caveat is that the fallback doesn't provide any indication of success so doesn't work inside of AuthFallbackViewController (you finish with a modal sitting there with Cancel and Back buttons). I've used an SFSafariViewController as that at least has a Done button for the user to tap when they've finished.

Deactivate-SIWA.mp4

Note: I've now removed the short period of time where the loading indicator disappeared in the recording.

[github-actions]

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[phloux]

Except the small issue with the changelog's file name, the other changes look good for me.

[ismailgulek]

Thanks, this was a pain. Just minor comments, otherwise LGTM!