Function set_app_menu 

pub fn set_app_menu(items: Vec<MenuItem>)

Set the application menu (menu bar / app-bar overflow / iPad main menu). Retains the model (post-injection — app_menu_model), injects the auto Preferences item when one is registered (docs/windows.md), drops the PREVIOUS app menu’s action closures (context menus share the map and are untouched), and forwards to the backend.