Add Window::show_window_menu

Add a method to request a system menu. The implementation
is provided only on Windows for now.

Co-authored-by: daxpedda <daxpedda@gmail.com>
Co-authored-by: Kirill Chibisov <contact@kchibisov.com>

src/platform_impl/ios/window.rs

@@ -198,6 +198,9 @@ impl Inner {
         Err(ExternalError::NotSupported(NotSupportedError::new()))
     }
 
+    #[inline]
+    pub fn show_window_menu(&self, _position: Position) {}
+
     pub fn set_cursor_hittest(&self, _hittest: bool) -> Result<(), ExternalError> {
         Err(ExternalError::NotSupported(NotSupportedError::new()))
     }