Initial Nim language support

[omentic]

Supercedes #3492.

I've not been able to find comprehensive tree-sitter documentation: and so the queries are mostly modelled after preexisting schemes of other languages.

Before this PR is merged, I'd like to:

• Test and debug the tree-sitter queries! They're unlikely to work first try. In particular: I'm worried about the type and variable declarations.
• regenerate documentation (cargo xtask docgen)

After this PR is merged, I'd like to:

• Incorporate these schemes into the tree-sitter-nim repository, so they can be reused across editors
• Help get alavass/tree-sitter-nim into a more complete state edit: aMOPel/tree-sitter-nim is now good enough
• Run the schemes by the Nim community and rework them into better, more complete representations as needed

Resources:

• alaviss/tree-sitter-nim: what the schemes were first based off of: it's incomplete but well-structured.
• aMOPel/tree-sitter-nim: a more complete but less clean grammar. I ended up rewriting the schemes in this.
• alaviss/rewrite: for the future.

[omentic]

Hmm, seems alaviss is working on a rewrite. I'm going to port the queries to aMOPel's repository to get a better sense of how they work, and then possibly re-port them back to alaviss's repo once it's done.

[omentic]

I have minimally working highlight queries + a working language server as of now. Keywords are much more involved and much closer tied to the grammar than I initially hoped. Types have been buggy, but I've some ideas for fixing them.

[omentic]

Everything but variable usages appear to be working.

[omentic]

@the-mikedavis This is ready to merge. May I request a review?

[the-mikedavis]

We don't currently support globs or regexes for roots. We might need something more powerful for Nim: from what I can see, Nim uses <projectname>.nimble for the manifest?

For now you can leave this as roots = [] and Helix will use the .git directory as the root.

[omentic]

@the-mikedavis I rebased on master and did some refactoring based on changes to upstream. This is now ready to merge (more than before).

There are a few known bugs:

• fixed: entries in std/[one, two] get highlighted as variables instead of namespaces
• fixed: the variables a and b in seq[tuple[a, b: int]] are accidentally matched as types

But that's it, as far as I've been able to test. Everything else is highlighted correctly.

[omentic]

Oh - indents are bugged, I think.

[omentic]

(ping @the-mikedavis)

[the-mikedavis]

Could you add a note on the Nim language server to the language server wiki? https://github.com/helix-editor/helix/wiki/How-to-install-the-default-language-servers