Hide rest of registration form if third-party login used

[rebecca-shoptaw]

Dependency to epic #7694. Subtask of #9315.

Problem

As part of an ongoing effort to clarify the registration flow, we want to hide the rest of the OL registration form if the user selects "Sign in with Google" and the third party login form grows.

This way, users will know which form to submit, but will still be able to return to the regular form by selecting "Cancel"

Expected behaviour / screenshots

Like the above, but the "OR" and everything below it would no longer appear.

Proposal & Constraints

Should hopefully be very simple, just intercepting the resize handler in ia_thirdparty_logins.js to add a quick display: none to the relevant divs. Similar to the approach in covers.js in #9418.

Related files

create.html
ia_thirdparty_logins.js

Stakeholders

@CDRI

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[cdrini]

We chatted and since this will only affect the case where a user already has an IA account, but no OL account, which is preeeetty niche, and there are a number of edge cases related to how to detect the IA iframe has expanded, and if the user has already entered information into the registration form; it seems like it's not worth the code.