FMenuBuilder::AddWrapperSubMenu

These classes need access to the [AddWrapperSubMenu()](API\Runtime\Slate\Framework\MultiBox\FMenuBuilder\AddWrapperSubMenu\1) methods friend class FWidgetBlock; friend class [FToolBarComboButtonBlock](API\Runtime\Slate\Framework\MultiBox\FToolBarComboButtonBlock); Adds a sub-menu which is a menu within a menu