Allow extensions to define more of the methods in the LspAdapter trait (#9554)

Our goal is to extract Svelte support into an extension, since we've
seen problems with the Tree-sitter Svelte parser crashing due to bugs in
the external scanner. In order to do this, we need a couple more
capabilities in LSP extensions:

* [x] `initialization_options` - programmatically controlling the JSON
initialization params sent to the language server
* [x] `prettier_plugins` - statically specifying a list of prettier
plugins that apply for a given language.
* [x] `npm_install_package`

Release Notes:

- N/A

---------

Co-authored-by: Marshall <marshall@zed.dev>
Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

crates/language/src/language_registry.rs

@@ -63,7 +63,7 @@ pub enum LanguageServerBinaryStatus {
 
 pub struct PendingLanguageServer {
     pub server_id: LanguageServerId,
-    pub task: Task<Result<lsp::LanguageServer>>,
+    pub task: Task<Result<(lsp::LanguageServer, Option<serde_json::Value>)>>,
     pub container_dir: Option<Arc<Path>>,
 }
 
@@ -629,6 +629,15 @@ impl LanguageRegistry {
             .unwrap_or_default()
     }
 
+    pub fn all_prettier_plugins(&self) -> Vec<Arc<str>> {
+        let state = self.state.read();
+        state
+            .languages
+            .iter()
+            .flat_map(|language| language.config.prettier_plugins.iter().cloned())
+            .collect()
+    }
+
     pub fn update_lsp_status(
         &self,
         server_name: LanguageServerName,
@@ -680,6 +689,12 @@ impl LanguageRegistry {
                     )
                     .await?;
 
+                let options = adapter
+                    .adapter
+                    .clone()
+                    .initialization_options(&delegate)
+                    .await?;
+
                 if let Some(task) = adapter.will_start_server(&delegate, &mut cx) {
                     task.await?;
                 }
@@ -727,18 +742,21 @@ impl LanguageRegistry {
                         })
                         .detach();
 
-                    return Ok(server);
+                    return Ok((server, options));
                 }
 
                 drop(this);
-                lsp::LanguageServer::new(
-                    stderr_capture,
-                    server_id,
-                    binary,
-                    &root_path,
-                    adapter.code_action_kinds(),
-                    cx,
-                )
+                Ok((
+                    lsp::LanguageServer::new(
+                        stderr_capture,
+                        server_id,
+                        binary,
+                        &root_path,
+                        adapter.code_action_kinds(),
+                        cx,
+                    )?,
+                    options,
+                ))
             }
         });