workspace: Handle non-cloneable items better (#41215)

When trying to split and clone a non clone-able workspace item we now
attempt split and move instead of doing nothing. Additionally we disable
the split menu buttons if we can't split the active item at all.

Release Notes:

- Improved handling of unsplittable panes

crates/extension_host/src/wasm_host.rs

@@ -69,6 +69,7 @@ pub struct WasmExtension {
     pub work_dir: Arc<Path>,
     #[allow(unused)]
     pub zed_api_version: SemanticVersion,
+    _task: Arc<Task<Result<(), gpui_tokio::JoinError>>>,
 }
 
 impl Drop for WasmExtension {
@@ -649,21 +650,26 @@ impl WasmHost {
 
             anyhow::Ok((
                 extension_task,
-                WasmExtension {
-                    manifest: manifest.clone(),
-                    work_dir: this.work_dir.join(manifest.id.as_ref()).into(),
-                    tx,
-                    zed_api_version,
-                },
+                manifest.clone(),
+                this.work_dir.join(manifest.id.as_ref()).into(),
+                tx,
+                zed_api_version,
             ))
         };
         cx.spawn(async move |cx| {
-            let (extension_task, extension) = load_extension_task.await?;
+            let (extension_task, manifest, work_dir, tx, zed_api_version) =
+                load_extension_task.await?;
             // we need to run run the task in an extension context as wasmtime_wasi may
             // call into tokio, accessing its runtime handle
-            gpui_tokio::Tokio::spawn(cx, extension_task)?.detach();
+            let task = Arc::new(gpui_tokio::Tokio::spawn(cx, extension_task)?);
 
-            Ok(extension)
+            Ok(WasmExtension {
+                manifest,
+                work_dir,
+                tx,
+                zed_api_version,
+                _task: task,
+            })
         })
     }