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

[francinelucca]

Closes https://github.com/github/primer/issues/4135

Changelog

New

• Overlay module css

Changed

• Refactor Overlay to use CSS modules when team feature flag is turned on
• Update SelectPanel import to new Overlay base component name (StyledOverlay -> BaseOverlay)

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: 4f5237e

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	102.83 KB (+0.09% 🔺)
packages/react/dist/browser.umd.js	103.2 KB (+0.18% 🔺)