Cleanup in Date component + formatDate expression

[olemartinorg]

Description

When implementing #1299 and #2122, I found a few problems with both the Date component and our formatDate expression function. Both fixed here:

1. The Date component did not properly use the current language to format the date (that matters for format tokens that print out the day of the week, for example). It was also lacking some error handling for when the format was unsupported (this was printed out to the user, not the developer).
2. The formatDate expression parsed dates by passing them to the new Date(str) constructor and hoping for the best. That works allright on frontend, but it makes it nearly impossible to implement the exact same date parsing on the backend. Instead I set up a list of regexes for input-formats we support, added lots of shared tests (including tests copied over from the JSON Schema project), along with tests for all the output-formats possible (according to our docs).
3. I added fairly generic support for a Date data type in the expression engine for this, so that the upcoming expressions for comparing dates can use the same functionality that is now used to parse dates for use in formatDate.

Related Issue(s)

• More expression functions #1299
• Dato i dynamikk med Expression #2122

Verification/QA

• Manual functionality testing
  • I have tested these changes manually
  • Creator of the original issue (or service owner) has been contacted for manual testing (or will be contacted when released in alpha)
  • No testing done/necessary
• Automated tests
  • Unit test(s) have been added/updated
  • Cypress E2E test(s) have been added/updated
  • No automatic tests are needed here (no functional changes/additions)
  • I want someone to help me make some tests
• UU/WCAG (follow these guidelines until we have our own)
  • I have tested with a screen reader/keyboard navigation/automated wcag validator
  • No testing done/necessary (no DOM/visual changes)
  • I want someone to help me perform accessibility testing
• User documentation @ altinn-studio-docs
  • Has been added/updated
  • No functionality has been changed/added, so no documentation is needed
  • I will do that later/have created an issue
• Support in Altinn Studio
  • Issue(s) created for support in Studio
  • This change/feature does not require any changes to Altinn Studio
• Sprint board
  • The original issue (or this PR itself) has been added to the Team Apps project and to the current sprint board
  • I don't have permissions to do that, please help me out
• Labels
  • I have added a kind/* label to this PR for proper release notes grouping
  • I don't have permissions to add labels, please help me out

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
63.3% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[bjosttveit]

Veldig grundig, som man jo må være med slike ting 💪