React v19 (with react-compiler)

[olemartinorg]

Description

This is now in a working state (although I haven't tested the performance difference, nor fixed all the eslint errors). Throwing it out there to get early feedback, and hopefully get the ball rolling a bit faster.

Yarn still complains about a few things:

➤ │ react is listed by your project with version 19.1.0 (pa1f6f), which doesn't satisfy what react-helmet-async and other dependencies request (but they have non-overlapping ranges!).
➤ │ react-dom is listed by your project with version 19.1.0 (p891d3), which doesn't satisfy what react-number-format (via @digdir/design-system-react) and other dependencies request (but they have non-overlapping ranges!).

Related Issue(s)

• closes React v19 #2861
• Update Designsystemet to latest v1 #2600

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/* and backport* label to this PR for proper release notes grouping
  • I don't have permissions to add labels, please help me out