Tooling Suggestion Checklist

• I have tried restarting my IDE and the issue persists.
• I have pulled the latest main branch of the repository.
• I have read and agree to Mocha's Code of Conduct and Contributing Guidelines
• I have searched for related issues and issues with the faq label, but none matched my issue.
• I want to provide a PR to resolve this

Overview

Mocha defines all code types with JSDoc comments in .js files right now. For example, this is how PluginDefinition is declared:

That type block becomes https://mochajs.org/api/global#PluginDefinition.

We'd like to move to .d.ts files for declaring these typedefs for a few reasons:

• It's a cleaner, less verbose, more readable syntax
• It makes 🚀 Feature: TypeScript .d.ts type declarations #4154 easier
• It makes 🛠️ Repo: Lint/validate JSDoc #4228 easier
• It makes 📝 Docs: Migrate /api docs or an equivalent from the old site to the new one #5309 easier

Additional Info

We're not committing to converting existing *.js files to *.ts - runtime source code will stay in JS-land for now. That's a separate discussion.