Add MenuBar.close()

[mvysny]

Describe your motivation

A PopupButton (a Button which shows a popup window with some rich layout on click) can easily be implemented via a MenuBar:

@Route("")
public class MainView extends VerticalLayout {

    public MainView() {
        final MenuBar menuBar = new MenuBar();
        final SubMenu fooSubMenu = menuBar.addItem("Foo").getSubMenu();
        final HorizontalLayout horizontalLayout = new HorizontalLayout(new Span("Popup button contents"));
        horizontalLayout.add(new Button("OK", e ->
                System.out.println("Clicked")));
        fooSubMenu.add(horizontalLayout);
        add(menuBar);
    }
}

The only problem is that, upon clicking on the "OK" button, the submenu stays open.

Describe the solution you'd like

It would be great to have a MenuBar.close() function which programmatically closes all open submenus. An implementation can be taken from vaadin/web-components#728 : we can simply call menuBar.getElement().executeJs("this._subMenu.close()"); from the server-side:

@Route("")
public class MainView extends VerticalLayout {

    public MainView() {
        final MenuBar menuBar = new MenuBar();
        final SubMenu fooSubMenu = menuBar.addItem("Foo").getSubMenu();
        final HorizontalLayout horizontalLayout = new HorizontalLayout(new Span("Popup button contents"));
        horizontalLayout.add(new Button("OK", e -> {
            System.out.println("Clicked");
            close(menuBar);
        }));
        fooSubMenu.add(horizontalLayout);
        add(menuBar);
    }

    private static void close(MenuBar menuBar) {
        menuBar.getElement().executeJs("this._subMenu.close()");
    }
}

Describe alternatives you've considered

No response

Additional context

No response

[mvysny]

Acceptance criteria: after menuBar.close() is called, none of its submenus are left open.