feat(BaseStyles): Convert BaseStyles to CSS modules behind team feature flag

[JelloBagel]

Closes https://github.com/github/primer/issues/4358

Changelog

Changed

• Convert BaseStyles to CSS modules behind primer_react_css_modules_team feature flag

Rollout strategy

• Patch release
• 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)

[changeset-bot]

🦋 Changeset detected

Latest commit: 0c6494f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@primer/react	Minor

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[github-actions]

👋 Hi, this pull request contains changes to the source code that github/github depends on. If you are GitHub staff, we recommend testing these changes with github/github using the integration workflow. Thanks!

[github-actions]

size-limit report 📦

Path	Size
packages/react/dist/browser.esm.js	103.71 KB (-0.06% 🔽)
packages/react/dist/browser.umd.js	104.23 KB (+0.13% 🔺)

[primer-integration]

👋 Hi from github/github! Your integration PR is ready: https://github.com/github/github/pull/353683

[primer-integration]

🔴 golden-jobs completed with status failure.

[JelloBagel]

Remaking to clean up PR: #5361