Fix CSS injection order

[bjosttveit]

Description

This is the only way I could find to fix the issues with CSS specificity, see the original issue for an explanation. This will override the document.head.appendChild method to inject style elements before any link elements. This means we no longer need to use !important or unecessarily great specificity to override styles from external libraries like material-ui and @digdir/design-system-react.

I also cleaned up the use of !important where I could.

Since our own css is now higher priority, this also means that the old tjenester3.css now more often gets applied over library styles, therefore a lot of cleanup in this file (-4000 lines) and affected components was necessary. This is a step in the right direction of getting rid of the old global css and the old font-icons. Whenever I broke an old component relying on tjenester3.css, I replaced them with design system components and nav icons instead of fixing them, so there are some visual updates as well.

Related Issue(s)

• closes CSS order prevents overriding design system #1000

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
• Changes/additions to component properties
  • Changes are reflected in both src/layout/layout.d.ts and layout.schema.v1.json, and these are all backwards-compatible
  • No changes made
• 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
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[bjosttveit]

Set as draft until I fix the visual changes

[sonarcloud]

SonarCloud Quality Gate failed.   

1 Bug
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

60.5% Coverage
0.0% Duplication

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[olemartinorg]

Phenomenal work!!