Update Babel dependencies to v8

[Copilot]

Updates Babel dependencies to v8 and adjusts repository build tooling for Babel 8 compatibility.

Changelog

New

• Added a changeset for published package impact.

Changed

• Updated Babel packages across the repo, including core, parser, presets, runtime, and transform plugins.
• Replaced Babel 7 proposal plugin usage with Babel 8-compatible transform plugins.
• Updated Babel parser usage where Babel 8 changed sync parsing APIs.
• Updated parser plugin lists to remove syntax plugins now handled by default.

Removed

• Removed incompatible babel-plugin-styled-components usage from build configs.

Rollout strategy

• Patch release
• Minor release
• Major release; @primer/mcp includes a Babel runtime major dependency update.
• None; if selected, include a brief description as to why

Testing & Reviewing

Review dependency, lockfile, and Babel config changes together. The key compatibility areas are build output generation and export graph parsing.

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-ui (Learn more about how to run integration tests)

[changeset-bot]

🦋 Changeset detected

Latest commit: 43ed04c

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

This PR includes changesets to release 2 packages

Name	Type
@primer/mcp	Major
@primer/styled-react	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

⚠️ Action required

👋 Hi, this pull request contains changes to the source code that github/github-ui depends on. If you are GitHub staff, test these changes with github/github-ui using the integration workflow. If this doesn't work, you can also use the original workflow here. Check the integration testing docs for step-by-step instructions. Or, apply the integration-tests: skipped manually label to skip these checks.

To publish a canary release for integration testing, apply the Canary Release label to this PR.

[joshblack]

@copilot this is not a major or minor change to packages. It's an internal update. This should not impact the public API of packages

[joshblack]

@copilot fix CI