Re-enable required account info modal on Ada CS

[mwtrew]

Re-enables required account info modal on Ada CS and centralises logic for which fields are required in validateFields, meaning the same logic is used for deciding which fields to show and checking the validity of the user object on submission. This creates a single source of truth for which fields are required across both sites, which will hopefully prevent validation and presentation logic from drifting apart in the future.

validateFields could also be used to simplify validation in signup and My Account, but I haven't included that in this PR. I will create a card for that.

Also replaces the old "big red text"-style error in the RAI modal with an ExigentAlert on both sites, which looks nicer.

[codecov]

Codecov Report

❌ Patch coverage is 73.52941% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 41.62%. Comparing base (423edfa) to head (daa8ed6).
⚠️ Report is 113 commits behind head on main.

Files with missing lines	Patch %	Lines
...lements/modals/RequiredAccountInformationModal.tsx	27.27%	8 Missing ⚠️
src/app/services/validation.ts	95.23%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1789      +/-   ##
==========================================
+ Coverage   41.58%   41.62%   +0.03%     
==========================================
  Files         535      534       -1     
  Lines       23509    23522      +13     
  Branches     6933     7786     +853     
==========================================
+ Hits         9776     9790      +14     
+ Misses      13692    13691       -1     
  Partials       41       41              

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[jacbn]

This looks great! I like the validity object. Couple of thoughts (not to action for this):

• When signing in with SSO currently we don't guide the user towards making a teacher account if that is what they want; they need to manually go to the teacher upgrade page. Given that this modal appears right after they first return to the site after completing SSO, the flow is now SSO => fill in RAI modal => upgrade to teacher => fill in RAI modal again for the teacher props (provided it shows up? the 50 mins before it appears probably won't have passed). It seems to me that after SSO but before the first appearance of the RAI modal we should have a student / teacher account type selection screen, but we can discuss this separately.
• When the form is invalid (particularly if the invalid field is one of the top ones), the error at the top is nice but can be hidden due to scrolling as the modal is quite tall. I would like to move to the other invalid model to fix this (this auto-scrolls to erroring fields), but again we should also be doing this on My Account so this can be separate.