Add language_server_workspace_configuration to extension API (#10212)

This PR adds the ability for extensions to implement
`language_server_workspace_configuration` to provide workspace
configuration to the language server.

We've used the Dart extension as a motivating example for this, pulling
it out into an extension in the process.

Release Notes:

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

---------

Co-authored-by: Max <max@zed.dev>
Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>

crates/extension/src/wasm_host/wit.rs

@@ -148,6 +148,25 @@ impl Extension {
         }
     }
 
+    pub async fn call_language_server_workspace_configuration(
+        &self,
+        store: &mut Store<WasmState>,
+        language_server_id: &LanguageServerName,
+        resource: Resource<Arc<dyn LspAdapterDelegate>>,
+    ) -> Result<Result<Option<String>, String>> {
+        match self {
+            Extension::V006(ext) => {
+                ext.call_language_server_workspace_configuration(
+                    store,
+                    &language_server_id.0,
+                    resource,
+                )
+                .await
+            }
+            Extension::V004(_) | Extension::V001(_) => Ok(Ok(None)),
+        }
+    }
+
     pub async fn call_labels_for_completions(
         &self,
         store: &mut Store<WasmState>,