Migrate remaining `core` package `.js` files (e.g. `lib/markdown-it/*.js`) to TypeScript and Upgrade Dependencies

[gerteck]

• Related issues: Migrate TypeScript Output from CommonJS (CJS) to ES Modules (ESM) - Epic #2615
• What is the area that this feature belongs to: Code Maintainence

TLDR: Migrate all core files to TypeScript to faciliate future switch from CommonJS (require/module.exports) to ESM (import/export) for consistency, type safety, and modern dependency support.

Is your feature request related to a problem? Please describe.

Currently, in #1913 we migrated the core package and most of its associated files to TypeScript, but left the files under lib/markdown-it/plugins as .js using CommonJS (require/module.exports).

Reasons to migrate these plugins to TypeScript now

1. Uniformity and consistency

   • The rest of the core package is now TypeScript. Keeping these plugins in JS breaks consistency and makes the codebase harder to maintain.

2. ESM interoperability

   • Some modern dependencies are ESM-only. Migrating plugins to TypeScript (and using import/export) facilitates smooth interop without relying on workarounds like dynamic import() or mixed module handling.

3. Type safety and better tooling

   • TypeScript provides static type checking, IDE auto-completion, and easier refactoring. Migrating these plugins improves developer experience and reduces the risk of runtime errors.

4. Future-proofing

   • As Node.js and modern tooling increasingly favor ESM, converting these plugins now reduces future migration pain and ensures compatibility with upcoming libraries and tooling

5. Dependency updates

   • Some plugins rely on older JS-only versions of dependencies (e.g., htmlparser2 v3). Migrating to TypeScript allows us to upgrade to newer versions that include types and ESM support, improving maintainability and ecosystem compatibility.

Proposed plan

• Convert lib/markdown-it/plugins/*.js → *.ts.
• Replace require/module.exports with import/export.
• Add TypeScript types where applicable.
• Update associated test files to .ts if necessary.
• Upgrade plugin dependencies to their latest ESM/TypeScript-compatible versions.

Impact

• No functional change; purely a migration for consistency, type safety, ESM interoperability, and future compatibility.

Describe the solution you'd like

Do the necessary

Describe alternatives you've considered

No response

Additional context

No response

[gerteck]

If all the files are migrated to .ts can gitignore and eslintignore all js files 👍