GetInvokingWindow() can only be used for the popup menus which have the invoking window, so add a new function which can be used to get the window associated with any kind of menu in all ports -- it already existed in wxMSW but is needed elsewhere too. git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64123 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775