Fix: core internal import in CJS legacy envs

[OEvgeny]

Fixes #

Changelog Entry

• Fixed core internal import in legacy CommonJS environments, in 5509, by @OEvgeny

Description

This adds missing files to the core npm package, so the internal module can be properly located in environments lacking exports field support.

Specific Changes

• Fixed files field to include top level js files

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• I have added tests and executed them locally
• I have updated CHANGELOG.md
• I have updated documentation

Review Checklist

This section is for contributors to review your work.

• Accessibility reviewed (tab order, content readability, alt text, color contrast)
• Browser and platform compatibilities reviewed
• CSS styles reviewed (minimal rules, no z-index)
• Documents reviewed (docs, samples, live demo)
• Internationalization reviewed (strings, unit formatting)
• package.json and package-lock.json reviewed
• Security reviewed (no data URIs, check for nonce leak)
• Tests reviewed (coverage, legitimacy)