Extract Haskell support into an extension (#9814)

This PR extracts Haskell support into an extension and removes the
built-in Haskell support from Zed.

I tested out the extension locally in a Nix shell using `nix-shell -p
ghc haskell-language-server` to confirm the language server still
operated as expected:

<img width="341" alt="Screenshot 2024-03-26 at 11 26 26 AM"
src="https://github.com/zed-industries/zed/assets/1486634/df16fd38-4046-4a45-ac9f-c2b85bffe5c0">

Release Notes:

- Removed built-in support for Haskell, in favor of making it available
as an extension. The Haskell extension will be suggested for download
when you open a `.hs` file.

crates/languages/src/lib.rs

@@ -23,7 +23,6 @@ mod elixir;
 mod elm;
 mod erlang;
 mod go;
-mod haskell;
 mod html;
 mod json;
 mod lua;
@@ -85,7 +84,6 @@ pub fn init(
         ("go", tree_sitter_go::language()),
         ("gomod", tree_sitter_gomod::language()),
         ("gowork", tree_sitter_gowork::language()),
-        ("haskell", tree_sitter_haskell::language()),
         ("hcl", tree_sitter_hcl::language()),
         ("heex", tree_sitter_heex::language()),
         ("html", tree_sitter_html::language()),
@@ -316,7 +314,6 @@ pub fn init(
         }
     }
 
-    language!("haskell", vec![Arc::new(haskell::HaskellLanguageServer {})]);
     language!(
         "html",
         vec![