fix(rollup): force .js extension for all files

[floryst]

All assets are considered js files. This ensures that bundlers treat
imports correctly, as some of the generated imports do not suffix with a
proper extension.

PR and Code Checklist

• semantic-release commit messages
• Run npm run reformat to have correctly formatted code

Context

Fixes #2072

Changes & Results

• [ESM] Forces all output chunks to end with .js

Testing

• This change adds or fixes unit tests
• All tests complete

[github-actions]

🎉 This PR is included in version 19.4.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[weeeina]

Hi @floryst, I really appreciate your prompt response to my bug #2072

Now, I get a brand new (and possibly related) import error:

Let me know if I should file another bug ticket for this. Again, thanks for responding so quickly!

Update: this seems to have resolved with a fresh local deployment. I'll follow up if I see it again.