Stop extensions' servers and message loops before removing their files (#34208)

Fixes an issue that caused Windows to fail when removing extension's
directories, as Zed had never stop any related processes.

Now:

* Zed shuts down and waits until the end when the language servers are
shut down

* Adds `impl Drop for WasmExtension` where does
`self.tx.close_channel();` to stop a receiver loop that holds the "lock"
on the extension's work dir.
The extension was dropped, but the channel was not closed for some
reason.

* Does more unregistration to ensure `Arc<WasmExtension>` with the `tx`
does not leak further

* Tidies up the related errors which had never reported a problematic
path before

Release Notes:

- N/A

---------

Co-authored-by: Smit Barmase <heysmitbarmase@gmail.com>
Co-authored-by: Smit <smit@zed.dev>

crates/extension_host/src/wasm_host.rs

@@ -54,7 +54,7 @@ pub struct WasmHost {
     main_thread_message_tx: mpsc::UnboundedSender<MainThreadCall>,
 }
 
-#[derive(Clone)]
+#[derive(Clone, Debug)]
 pub struct WasmExtension {
     tx: UnboundedSender<ExtensionCall>,
     pub manifest: Arc<ExtensionManifest>,
@@ -63,6 +63,12 @@ pub struct WasmExtension {
     pub zed_api_version: SemanticVersion,
 }
 
+impl Drop for WasmExtension {
+    fn drop(&mut self) {
+        self.tx.close_channel();
+    }
+}
+
 #[async_trait]
 impl extension::Extension for WasmExtension {
     fn manifest(&self) -> Arc<ExtensionManifest> {
@@ -742,7 +748,6 @@ impl WasmExtension {
     {
         let (return_tx, return_rx) = oneshot::channel();
         self.tx
-            .clone()
             .unbounded_send(Box::new(move |extension, store| {
                 async {
                     let result = f(extension, store).await;