GTK4: dw_menu_popup() coordinates are relative to the parent window. The coordinates in the context events in GTK4 had been relative to the container or tree widget, causing the menu to popup in offset locations. Added a function to convert from the widget coordinate to the window. The events now pass window relative coordinates so when passed to dw_menu_popup() the menu appears in about the right location.

This is a file just to keep this directory in existance in CVS.