gpui: Flash menu in menubar on macOS when action is triggered (#38588)

On macOS, traditionally when a keyboard shortcut is activated, the menu
in the menu bar flashes to indicate that the action was recognised.

<img width="289" height="172" alt="image"
src="https://github.com/user-attachments/assets/a03ecd2f-f159-4f82-b4fd-227f34393703"
/>

This PR adds this functionality to GPUI, where when a keybind is pressed
that triggers an action in the menu, the menu flashes.

Release Notes:

- N/A

crates/gpui/src/platform/windows/platform.rs

@@ -536,6 +536,8 @@ impl Platform for WindowsPlatform {
             .validate_app_menu_command = Some(callback);
     }
 
+    fn on_action_triggered(&self, _action: &dyn Action) {}
+
     fn app_path(&self) -> Result<PathBuf> {
         Ok(std::env::current_exe()?)
     }