Add support for Agda (#8285)

* agda language support (wip)

* improve highlights

* disable agda-language-server

* minor addendum to documentation

* cargo xtask docgen

* oh i can just do this neat

* minor comment cleanup

* upstream updated

* imports: missed a spot

---------

Co-authored-by: Michael Davis <mcarsondavis@gmail.com>

book/src/generated/lang-support.md

@@ -1,5 +1,6 @@
 | Language | Syntax Highlighting | Treesitter Textobjects | Auto Indent | Default LSP |
 | --- | --- | --- | --- | --- |
+| agda | ✓ |  |  |  |
 | astro | ✓ |  |  |  |
 | awk | ✓ | ✓ |  | `awk-language-server` |
 | bash | ✓ | ✓ | ✓ | `bash-language-server` |

book/src/guides/adding_languages.md

@@ -36,6 +36,7 @@ below.
 3. Refer to the
    [tree-sitter website](https://tree-sitter.github.io/tree-sitter/syntax-highlighting#queries)
    for more information on writing queries.
+4. A list of highlight captures can be found [on the themes page](https://docs.helix-editor.com/themes.html#scopes).
 
 > 💡 In Helix, the first matching query takes precedence when evaluating
 > queries, which is different from other editors such as Neovim where the last
@@ -51,3 +52,4 @@ below.
   grammars.
 - If a parser is causing a segfault, or you want to remove it, make sure to
   remove the compiled parser located at `runtime/grammars/<name>.so`.
+- If you are attempting to add queries and Helix is unable to locate them, ensure that the environment variable `HELIX_RUNTIME` is set to the location of the `runtime` folder you're developing in.