Registration broken during UI Auth process

[clokep]

As part of #5667 we made quite a few changes to the UI Authentication process and some of these changes broke registration for riot-ios and riot-android (riotx was not affected). When attempting to register with those the user would be shown the "Requested operation has changed during UI authentication session" error added in #7068. Additionally #7268 made some changes which caused an updated client dict to be ignored.

This was noticed after a deploy on May 1 to matrix.org.

The specification is somewhat unclear whether the parameters in the client dict should be provided for each request during registration (a UI authentication cycle), although it does suggest they should be:

It does this by resubmitting the same request with the addition of an auth key in the object that it submits.

[clokep]

Fixed per #7455.