Fix Windows Rollup build

[markdalgleish]

This addresses a couple of issues in the Rollup build on Windows:

• rollup-plugin-extensions doesn't resolve paths correctly on Windows, so we need to replace it with @rollup/plugin-node-resolve.
• rollup-plugin-copy doesn't support absolute paths on Windows.

[changeset-bot]

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Latest commit: e872c86

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[github-actions]

🤖 Hello there,

We just published version 6.28.2-pre.0 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

Thanks!