ESM Version of `theme-preval.js` is actually CommonJS

[dgreif]

Describe the bug

PRC is currently built with exports for both commonjs and esm, with the esm version located in lib-esm. Unfortuantely the theme-preval.js file included in lib-esm is still using commonjs export syntax, which causes it to break environments that only understand ESM.

To Reproduce
Steps to reproduce the behavior:

1. Run npm run build
2. Observe the lib-esm/theme-preval.js file has commonjs exports like the following:

module.exports = {
  "theme": {
    // theme output here
  }
}

Expected behavior
The build should output an esm compatible version of theme-preval.js with a named export

export const theme = {
  // theme output here
}

[siddharthkp]

Trying to triage this and this is the first line that I saw 😅: https://github.com/primer/react/blob/main/src/theme-preval.js#L2

Any tips on how can we make this esm compatible with preval? Maybe a tiny script that manipulates the file during build time?

[dgreif]

@siddharthkp sorry I didn't see your comment earlier, I've got a PR up that uses babel to handle the conversion. Alternatively, we could write a script that handles this specific case. I'm open to either approach 😄