Implement formatter playground

[Zuruuh]

📌 What Does This PR Do?

Very simple implementation of a formatter playground. It doesn't support any configuration for now but definitely doable (would require server side changes though)

🔍 Context & Motivation

I'm working on integrating the formatter in my codebases and it would be easier to have a playground link to easily isolate, reproduce, and demonstrate the bugs I'd want to report.

🛠️ Summary of Changes

• Add a new (sub)tabs system to the playground
• Implement the formatter tab separately from the linter+analyzer one
• Added lld to the nix flake, since it's required to build the mago wasm binary

📂 Affected Areas

• Linter
• Formatter
• CLI
• Composer Plugin
• Dependencies
• Documentation
• Other (please specify):

📝 Notes for Reviewers

The code was mostly generated through AI to be honest since I have very few experience with vue, however I did re-read it, refactor, and tested it locally 👍