Looks for a match between the supported targets of
context and the
dest_target_list, returning the first matching
target, otherwise returning gdk_none.
dest_target_list should usually be the return value from
drag_dest_get_target_list, but some widgets may have different valid targets for different parts of the widget; in that case, they will
have to implement a drag_motion handler that passes the correct target list to this function.
drag destination widget
list of droppable targets, or null to use gtk_drag_dest_get_target_list ( this).
first target that the source offers and the dest can accept, or gdk_none