world: extend docs around classes and functions, support generics for parameters

[davidjgoss]

🤔 What's changed?

• Update the world documentation to cover worlds as plain functions
• Update the world documentation to cover TypeScript stuff
• Add support for generics for world parameters on world-related interfaces and classes

⚡️ What's your motivation?

Fixes #1968.

🏷️ What kind of change is this?

• 🏦 Refactoring/debt/DX (improvement to code design, tooling, documentation etc. without changing behaviour)
• ⚡ New feature (non-breaking change which adds new behaviour)

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct
• I've changed the behaviour of the code
  • I have added/updated tests to cover my changes.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• Users should know about my change
  • I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

---

This text was originally generated from a template, then edited by hand. You can modify the template here.

[coveralls]

Coverage remained the same at 98.238% when pulling 9c8de6f on fix/docs-typescript-world-fn into c45330a on main.