Function submenu_button 

pub fn submenu_button<R>(
    ui: &mut Ui,
    parent_state: Arc<RwLock<MenuState>>,
    title: impl Into<WidgetText>,
    add_contents: impl FnOnce(&mut Ui) -> R,
) -> InnerResponse<Option<R>>

👎Deprecated: Use egui::containers::menu instead

Construct a nested sub menu in another menu.

Opens on hover.

Returns None if the menu is not open.