Add Dune (OCaml build system)

[kisaragi-hiu]

Description

Dune is a build system for OCaml, used in a large number of OCaml projects. This PR adds classification and syntax highlighting support for it.

I specified ace_mode: lisp because Dune is an Sexp-based language. I'm guessing that this is appropriate.

Checklist:

• I am adding a new language.
  • The extension filename of the new language is used in hundreds of repositories on github.com.
    • Search results for each file name:
      • https://github.com/search?type=code&q=NOT+is%3Afork+path%3A%2F%5Edune%24%2F
        • This was not deemed to be enough uses, and I'm fine with leaving it out.
      • https://github.com/search?type=code&q=NOT+is%3Afork+path%3A%2F%5Edune-file%24%2F
        • This one is probably justified as it's used by Dune itself, even if just once.
        • This has now been removed from this PR.
      • https://github.com/search?type=code&q=NOT+is%3Afork+path%3A%2F%5Edune-project%24%2F
      • https://github.com/search?type=code&q=NOT+is%3Afork+path%3A%2F%5Edune-workspace%24%2F
        • "dune-workspace" is the name that has a special meaning in Dune, but it's more common to write it in dune-workspace.dev then explicitly tell Dune to use that file.
        • This is not popular enough and have been left out of this PR.
      • https://github.com/search?type=code&q=NOT+is%3Afork+path%3A%2F%5Edune-workspace%5C.dev%24%2F
        • This is not popular enough and have been left out of this PR.
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • dune-project
    • Sample license(s):
      • reasonml/reason
  • I have included a syntax highlighting grammar: https://github.com/maelvls/vscode-dune
    • ocamllabs/vscode-ocaml-platform might be more suitable in the long run, but it errored out when I tried to add it. It also provides grammars for OCaml itself within the same repository, which makes using it more complicated right now.
  • I have added a color
    • Hex value: #89421e
    • Rationale: This is the main color of the Dune logo.
  • I have updated the heuristics to distinguish my language from others using the same extension.

[lildude]

Marking as pending popularity as the two workspace files aren't sufficient yet.

[lildude]

Reviewing this with fresh eyes, I don't think it makes sense splitting this out into different languages. They all share the same grammar and are grouped together so it makes sense to put them all into a single Dune language definition.

I note you've manually set each entry in this PR with a different scopes, however the upstream grammar only has a single source.dune so your other scopes won't work. This also further confirms these are all the same language so don't need separate entries.

Please merge these languages into a single Dune language.

[kisaragi-hiu]

Merged the three previously declared languages into one and rebased onto master.

The split was left over from when I was trying to use ocamllabs/vscode-ocaml-platform (which has the split for different vocabulary), and I left it in by mistake when I switched to maelvls/vscode-dune due to errors when I tried the former.

Changes applied. Pending popularity of everything but the dune-project file.

[lildude]

As an FYI, dune-project currently meets our usage requirements. dune is close. The other two are miles off. In short, everything but dune-project is preventing this PR from being merged.

If you want, you can make this PR just for dune-project and add support for the others as popularity grows. User will be able to use an override in the meantime.

[kisaragi-hiu]

I've dropped the other three file names besides dune-project. Evidently I've misjudged the usage requirements to be way lower than what they actually are.