add wxSYS_DCLICK_TIME system metric constant; use it for the generic list control rename timer interval (patch 1782472)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@48622 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/settings.cpp

@@ -494,6 +494,12 @@ int wxSystemSettingsNative::GetMetric( wxSystemMetric index, wxWindow* win )
 
             return dclick_distance * 2;
 
+        case wxSYS_DCLICK_MSEC:
+            gint dclick;
+            g_object_get(gtk_settings_get_default(),
+                            "gtk-double-click-time", &dclick, NULL);
+            return dclick;
+
         case wxSYS_DRAG_X:
         case wxSYS_DRAG_Y:
             gint drag_threshold;