focusNode property
An optional focus node to use as the focus node for the menu.
If one is not supplied, then one will be automatically allocated, owned, and managed by the menu. The menu
will be focusable even if a focusNode is not supplied. If supplied, the given focusNode will be hosted by the
menu but not owned. See FocusNode for more information on what being hosted and/or owned implies.
Supplying a focus node is sometimes useful if an ancestor to the menu wants to control when the menu has the focus. The owner will be responsible for calling FocusNode.dispose on the focus node when it is done with it, but the menu will attach/detach and reparent the node when needed.
Implementation
final FocusNode? focusNode;