Docs: Document default values for turbopack.resolveExtensions #98609

What is the documentation issue?

The resolveExtensions docs say the array replaces the defaults rather than extending them, but never list what the defaults are.

Without that list, users can't safely override the option - dropping an extension breaks resolution in ways that are hard to debug.

Please add the default extensions to the page, or a link to the source where they are defined.

Is there any context that might help us understand?

The docs explicitly warn that the supplied array replaces the defaults rather than extending them:

This overwrites the original resolve extensions with the provided list. Make sure to include the default extensions.

Does the docs page already exist? Please link to it.

https://nextjs.org/docs/app/api-reference/config/next-config-js/turbopack#resolving-custom-extensions