Add support for gherkin with markdown

[Zayon]

See https://github.com/cucumber/gherkin/blob/main/MARKDOWN_WITH_GHERKIN.md

🤔 What's changed?

Added support for .feature.md (Markdown-with-Gherkin) in LSP services

⚡️ What's your motivation?

My ultimate goal is to make ide extension support this syntax, I have a working setup for vscode (syntax highlight, autocomplete, goto definition)

🏷️ What kind of change is this?

• ⚡ New feature (non-breaking change which adds new behaviour)

♻️ Anything particular you want feedback on?

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct
• I've changed the behaviour of the code
  • I have added/updated tests to cover my changes.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• Users should know about my change
  • I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

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[Zayon]

Enregistrement.de.l.ecran.2026-04-15.a.18.15.41.mov