Refresh README elements including broken links

[kieran-ryan]

🤔 What's changed?

• Fixed broken links
• Updated commented language names of samples to headers
• Updated language test statuses to live GitHub workflow badges
• Updated all diagrams to Mermaid

⚡️ What's your motivation?

• Several links were broken, including https://ndjson.org which although appeared to be an official link, is now being used for link farming (e.g. links to gambling sites)
• Change commented language names in sample code blocks to headers allows users to link and share to them directly
• Live test status badges is perhaps a more succinct and accurate (live) reflection of language test status
• The AST diagram is now in mermaid. Updated the rest to mermaid for consistency and as it may be easier to update and maintain.

🏷️ What kind of change is this?

• 📖 Documentation (improvements without changing code)

♻️ Anything particular you want feedback on?

• Is there anything particularly outdated in the changes that should be updated with this change? e.g. the diagrams
• Anything that should be split from this PR or perhaps inadvisable to change at this time?

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct

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[olleolleolle]

Thanks for the cleaning up!