Gleam: add support for built-in language server (helix-editor#3139)

* Add gleam lsp support

* Docgen gleam lsp support

Author: connorlay

book/src/generated/lang-support.md

@@ -30,7 +30,7 @@
 | git-diff | ✓ |  |  |  |
 | git-ignore | ✓ |  |  |  |
 | git-rebase | ✓ |  |  |  |
-| gleam | ✓ | ✓ |  |  |
+| gleam | ✓ | ✓ |  | `gleam` |
 | glsl | ✓ | ✓ | ✓ |  |
 | go | ✓ | ✓ | ✓ | `gopls` |
 | gomod | ✓ |  |  | `gopls` |

languages.toml

@@ -1140,6 +1140,7 @@ file-types = ["gleam"]
 roots = ["gleam.toml"]
 comment-token = "//"
 indent = { tab-width = 2, unit = "  " }
+language-server = { command = "gleam", args = ["lsp"] }
 
 [[grammar]]
 name = "gleam"