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/extensions_ui/src/extension_suggest.rs

@@ -32,6 +32,7 @@ pub fn suggested_extension(file_extension_or_name: &str) -> Option<Arc<str>> {
                 ("gleam", "gleam"),
                 ("graphql", "gql"),
                 ("graphql", "graphql"),
+                ("haskell", "haskell"),
                 ("java", "java"),
                 ("kotlin", "kt"),
                 ("latex", "tex"),