Syntax highlight for `*.astro` files

[AriPerkkio]

Is your feature request related to a problem?

*.astro files are displayed without any syntax highlighting in the CodeMirror editor. https://astropatterns-dev.vercel.app

Describe the solution you'd like.

Add syntax highlight similar to:

• feat: add Vue language to CodeMirror #256
• feat: add Svelte language to CodeMirror #212

Describe alternatives you've considered.

Additional context

Split from #144.

[eric-burel]

There are bounties on this because the problem is that we lack an Astro grammar in the first place in codemirror official packages (where Vue support comes from) or Replit packages (where Svelte come from):

• https://replit.com/bounties/@masfrost/astro-and-astro-mark
• https://replit.com/bounties/@triptych/get-astro-language-s

So it seems that these packages rely on a simple grammar describing the language: it must exist in Astro VS code extension/language server, not sure about the formats though.