Convert Caret component to CSS modules

[jonrohan]

Closes https://github.com/github/primer/issues/4035

This component has a usage of 0 according to primer query and the primary internal usage PointerBox has 6 uses from primer query. Because these numbers are so low, I figured it was safe to go directly to CSS modules.

Changelog

Changed

Convert Caret component to CSS modules

Rollout strategy

• [ ] Patch release
• [x] Minor release
• [ ] Major release; if selected, include a written rollout or migration plan
• [ ] None; if selected, include a brief description as to why

Testing & Reviewing

Merge checklist

• [ ] Added/updated tests
• [ ] Added/updated documentation
• [ ] Added/updated previews (Storybook)
• [ ] Changes are SSR compatible
• [ ] Tested in Chrome
• [ ] Tested in Firefox
• [ ] Tested in Safari
• [ ] Tested in Edge
• [ ] (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)