Type of Improvement

Refactoring code

Proposal

We should use ESM imports instead of CommonJS.
See: https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c

Related issues:

• markdownlint-cli2 commit: Remove references to ESM/.mjs because VS Code only supports it during development
• markdownlint-cli2 issue: Attempt to load .mjs configuration file fails with "Invalid host defined options"
• VSCode: Enable consuming of ESM modules in extensions

Rename eslint.config.mjs to eslint.config.js.