docs: complete loader context API doc and JSDoc

[chenjiahan]

Summary

• Complete loader context API documentation.
• Add JSDoc for the LoaderContext type.
• Add an example of TypeScript loader.

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

[netlify]

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[codspeed-hq]

CodSpeed Performance Report

Merging #9478 will not alter performance

_{Comparing loader_context_doc_0226 (5bd6f7e) with main (4508a5e)}

🎉 Hooray! codspeed-node just leveled up to 4.0.0!

A heads-up, this is a breaking change and it might affect your current performance baseline a bit. But here's the exciting part - it's packed with new, cool features and promises improved result stability 🥳!
Curious about what's new? Visit our releases page to delve into all the awesome details about this new version.

Summary

✅ 7 untouched benchmarks