docs(package-json): add documentation for type field

[MaxBlack-dev]

Description

This PR adds documentation for the type field in package.json, which controls whether Node.js treats .js files as ES modules or CommonJS modules.

Changes

• Added a new section documenting the type field
• Explained the two possible values: module and commonjs
• Provided examples for both module types
• Added a note about .mjs and .cjs file extensions
• Linked to Node.js official documentation

Fixes

Closes #8376

Context

The type field is a crucial part of package.json for modern Node.js projects, especially with the widespread adoption of ES modules. As reported in issue #8376, this field was not documented in npm's package.json reference, which caused confusion for developers trying to understand how to configure their packages for ESM or CommonJS.

This documentation clarifies:

1. How to enable ES modules in a package ("type": "module")
2. How to explicitly use CommonJS ("type": "commonjs")
3. The default behavior when type is omitted (CommonJS)
4. That file extensions (.mjs/.cjs) override the type field

Type of Change

• Documentation update

[wraithgar]

This likely needs a discussion. There is a similar PR on the docs themselves for the type field that has the context. The TLDR is that Node.js drives this field, npm does not parse it at all so the docs need to point to the source, and not try to recreate it in a way that needs maintenance on our end.

ETA: added context to the issue too #8376 (comment)

[MaxBlack-dev]

@wraithgar Thank you for the feedback! I've updated the PR to follow the same approach discussed in npm/documentation#1653 - the documentation now simply references the Node.js documentation as the source of truth, avoiding technical details that would need maintenance. Please let me know if this approach works better.