Make GitRepository::status async and remove cx parameter (#27514)

This lays the groundwork for using `status` as part of the new agent
panel.

Release Notes:

- N/A

crates/zed/src/main.rs

@@ -264,7 +264,7 @@ fn main() {
         };
     log::info!("Using git binary path: {:?}", git_binary_path);
 
-    let fs = Arc::new(RealFs::new(git_binary_path));
+    let fs = Arc::new(RealFs::new(git_binary_path, app.background_executor()));
     let user_settings_file_rx = watch_config_file(
         &app.background_executor(),
         fs.clone(),