Reorganize JS for registration form and add loading indicator

[rebecca-shoptaw]

Closes #9603.

Feature. Reorganizes registration validation js to add a loading indicator at the correct point in the validation process and remove the delay between submission and validation.

Technical

Fairly simple! Involved moving the recaptcha info to a div with data-size="invisible" per the recaptcha docs and adjusting the order of the JS checks.

The original grecaptcha.execute() implementation was nested in a click handler rather than a submit handler, as the latter never actually fired, but I'm hoping that now that the recaptcha is no longer linked directly to the submit button a submit handler should work just fine.

Testing

1. Go to /account/create
2. Enter badly formatted and/or incomplete data and hit submit (either directly or by hitting enter)
3. The submit button should remain enabled and you should immediately see an HTML error pop up
4. Fix the entires and submit again
5. The submit button should become disabled and replaced with the text "Loading..." and after a couple seconds, the page should refresh

Results of partial GitPod testing:
With the line grecaptcha.execute() replaced with signupForm.submit() since it doesn't work locally:
✅ If all inputs are valid, the submit button becomes a loading indicator and then the page refreshes
✅ HTML errors appear immediately following submit button press, and the submit button does not become a loading indicator

Screenshot

Stakeholders

@cdrini

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 22.22222% with 7 lines in your changes missing coverage. Please review.

Project coverage is 17.08%. Comparing base (ce16a79) to head (9cbd068).
Report is 453 commits behind head on master.

Files with missing lines	Patch %	Lines
openlibrary/plugins/openlibrary/js/signup.js	22.22%	5 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9604      +/-   ##
==========================================
+ Coverage   16.06%   17.08%   +1.02%     
==========================================
  Files          90       89       -1     
  Lines        4769     4730      -39     
  Branches      832      829       -3     
==========================================
+ Hits          766      808      +42     
+ Misses       3480     3412      -68     
+ Partials      523      510      -13     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[cdrini]

Nice! This makes so much more sense to do this way. All my tests pass!

Test:

• ✅ Entering a used email shows error
• ✅ Entering a user username shows error
• ✅ Hitting submit while error visible does nothing
• ✅ Entering everything correctly and hitting submit shows loading
• ✅ Entering everything correctly and hitting submit creates account

With JS Disabled:

• ✅ Hitting submit while error visible reloads with errors visible
• 🏳 Entering everything correctly and hitting submit seems to not create an account
  • Pre-existing problem on production page