Add theme support for form validation

[britneywwc]

Done

• Depends on new custom colour variables: Export status color variables as CSS custom properties #4979
• Added theme support for form validation: success, error, warning

QA

• Open demo
• Go to /docs/examples/patterns/forms/form-validation and /docs/examples/patterns/forms/form-validation-dark
• Check if stylings are similar.
• Additionally, try to change the theme on body tag to see changes.

Check if PR is ready for release

If this PR contains Vanilla SCSS code changes, it should contain the following changes to make sure it's ready for the release:

• PR should have one of the following labels to automatically categorise it in release notes:
  • Feature 🎁, Breaking Change 💣, Bug 🐛, Documentation 📝, Maintenance 🔨.
• Vanilla version in package.json should be updated relative to the most recent release, following semver convention:
  • if CSS class names are not changed it can be bugfix relesase (x.x.X)
  • if CSS class names are changed/added/removed it should be minor version (x.X.0)
  • see the wiki for more details
• Any changes to component class names (new patterns, variants, removed or added features) should be listed on the what's new page.

Screenshots

[if relevant, include a screenshot or screen capture]

[webteam-app]

Demo starting at https://vanilla-framework-4981.demos.haus

[bartaz]

Please use --tinted-borders colors for all icons, dark and light.

[bartaz]

Thanks!