Add support for Agda

[omentic]

supersedes #3092

todo:

• try to get the updated tree-sitter code upstreamed (instead of relying on my fork)
  • Unbreak tree-sitter tree-sitter/tree-sitter-agda#19
• make queries better
  • properly match functions
  • more fine-grained matching of types, ex. (expr (expr (expr... (atom) @type)))
    • lost cause, see Specify descendant or ancestor in query tree-sitter/tree-sitter#880
• indentation queries?

[omentic]

Syntax highlighting just about working. Trying to get functions working, then I think this'll be ready to merge.

The language server does not appear to work at all, unfortunately. I might remove it or leave it in with a note.

[omentic]

This PR is ready for review. I may have a follow-up sometime adding proper function highlighting & als support, the former appears to be a legitimate upstream bug and the latter still a mystery.

@the-mikedavis can you squash merge this or would you prefer me to rebase?

[the-mikedavis]

We can squash + merge this, no need to rebase

[Septias]

Is this stalling?

[omentic]

It's done on my end, I've been running it locally for a while. The syntax highlighting is unfortunately pretty terrible - but it's nothing that can be addressed until tree-sitter/tree-sitter#880 is addressed. Any more specificity with regard to types kills performance exponentially (> 3 ish is unusable) and breaks highlighting for nested types above a certain level.

[Septias]

Do you use it regularly and would you advise others to do so aswell? @omentic

[omentic]

I mean, it's fine, it looks just like the above picture. I do not write Agda regularly in Helix and I would not advise others to do so as well because Helix lacks support for Unicode input, and Unicode input is required to write Agda.

When a snippets system lands, it'd be fine, I guess: but without a "proof assistant mode" or similar not great.

[pascalkuthe]

This needs co flicts resolved before being g merged

[omentic]

(tangential re: a proof assistant mode: it's very likely it could piggyback off of debug mode, before or after a redesign. i've had no time to poke around and prototype something, unfortunately, but might in the far future...)