Remove checkbox & radio base styles

[sowasred2012]

Done

• Moved base checkbox & radio styles to pattern, and dropped support for base styles
• Removed base examples
• Added notes to upgrade guide about using the pattern instead
• Moved the indeterminate example to patterns

QA

• Open demo
• Look for checkbox and radio examples in the Base column, see that there are none
• View all checkbox and radio examples in the Pattern column (including the alignment example), see that there are no base elements and that the examples aren't broken.
• Review updated documentation:
  • Forms - Checkbox
  • Forms - Radio
  • Upgrade guide

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.
• Documentation side navigation should be updated with the relevant labels.

[webteam-app]

Demo starting at https://vanilla-framework-4072.demos.haus

[bartaz]

This is likely not related to this PR (this bug seems to be on live version of Vanilla), but seems we missed it and could be fixed now:

Muted heading variant of radio button doesn't use muted text color.