SelectPanel: Implement full variant for narrow screens

[broccolinisoup]

Closes https://github.com/github/primer/issues/4109

Changelog

New

• Introducing full-variant to the current SelectPanel. This is not a prop/option to choose; it is a default behaviour when the screen is narrow to accommodate more content due to accessibility concerns.
• "Close (X)" button

Changed

• Refactored SelectPanel to use StyledOverlay instead of AnchoredOverlay to accomodate both anchored and full-screen styles via css.

Removed

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

You can test this behaviour on any story when the screen is narrow.

[changeset-bot]

⚠️ No Changeset found

Latest commit: e2055fb

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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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	99.11 KB (+0.54% 🔺)
packages/react/dist/browser.umd.js	99.42 KB (+0.54% 🔺)

[primer-integration]

🟢 golden-jobs completed with status success.

[primer-integration]

👋 Hi from github/github! Your integration PR is ready: https://github.com/github/github/pull/349615