Now that we have OverlayPortal, we should rewrite the MenuAnchor cascading menus to use it. It would help with issues like #36445 and with issues where defining the semantics of a menu system (like the semantics traversal order) rely on defining something above a widget in the widget tree.

Currently, it's not possible to define the semantics order for items in a submenu because the submenu is actually in the overlay, and not a child of the menu button.