Add a method allowing creation of a wxMenu object from a native menu handle. This will be used to implement access to the system menu in an upcoming commit but could also be useful for other purposes. git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68595 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775