Fixes and updates to post-UIA callbacks

This MR lays the groundwork for switching away from our current .onLoggedIn() and .onEnrolled() callbacks in the UIA system. Instead, each auth checker now implements a single .onSuccess() function that, in the future, will be called every time UIA completes. It will be the responsibility of the auth checker to decide when to take what actions in .onSuccess(), depending on the user and the "real" Matrix API request that has been UIA'd.

In the meantime, this MR fixes the list of endpoints for which we should call the .onEnrolled() callback, to enable changing passwords or email addresses, etc.