This is useful when e.g. resetting both secret storage and cross-signing
together, as it avoids prompting for the secret storage key that was just
created.
This changes to uploading cross-signing keys first, since they require a valid
UI auth session, and so are more likely to fail than other API calls. With the
new ordering, if they do fail, then by failing first, we won't have made any
changes to the user's account, so everything rolls back correctly.
In order to handle auth errors (such as incorrect passwords), we need to ensure
we only try to upload cross-signing keys from within the auth flow helper
function.
This rearranges things to store that function in the builder to use it when the
actual upload happens.
This is to better support the react-sdk in trying to identify what actually changed in settings instead of re-firing everything.
Overall this change differs from `prev_content` semantics as it's the last known *stored* event, not whatever the server thinks may or may not have changed.
J. Ryan Stinnett