Extract Erlang support into an extension (#9974)

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

Tested using a Nix shell:

```
nix-shell -p erlang-ls
```

Release Notes:

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

crates/extensions_ui/src/extension_suggest.rs

@@ -19,6 +19,8 @@ fn suggested_extensions() -> &'static HashMap<&'static str, Arc<str>> {
             ("csharp", "cs"),
             ("dockerfile", "Dockerfile"),
             ("elisp", "el"),
+            ("erlang", "erl"),
+            ("erlang", "hrl"),
             ("fish", "fish"),
             ("git-firefly", ".gitconfig"),
             ("git-firefly", ".gitignore"),