Add Tidy Formatter (Formatting & Beautification)

[L3gatum]

Adds Tidy Formatter to the Formatting & Beautification section.

It's a safe, consent-first multi-language beautifier for JavaScript, TypeScript, JSX/TSX, CSS, SCSS, LESS, HTML and JSON. It only formats on demand (never hooks save, never makes itself the default formatter) and refuses to write any output that isn't provably equivalent to the original — so it can't silently corrupt code. It's a maintained alternative to the long-abandoned JS-CSS-HTML Formatter.

• Marketplace: https://marketplace.visualstudio.com/items?itemName=ced-lab.tidy-formatter
• Open VSX: https://open-vsx.org/extension/ced-lab/tidy-formatter
• Repo (MIT): https://github.com/ced-lab-gh/tidy-formatter

The entry follows the CONTRIBUTING format (## [Name](marketplace-url) + > description) and is added to the section's table of contents. Disclosure: I'm the author.