app: in prop-GUI, use "direction" UI-meta of angle props for dial

When constructing a prop-GUI widget for an angle property with a
dial, use the the property's "direction" UI-meta, if exists, to set
the direction of the dial.  Together with GEGL commit
7b0578073a0f20334b5a8a8fe57b649d9f302454, this fixes wrong dial
direction in certain ops that use clockwise angles.

app/propgui/gimppropgui.c

@@ -211,6 +211,9 @@ gimp_prop_widget_new_from_pspec (GObject                  *config,
           gtk_widget_show (widget);
 
           dial = gimp_prop_angle_dial_new (config, pspec->name);
+          g_object_set (dial,
+                        "clockwise-angles", HAS_KEY (pspec, "direction", "cw"),
+                        NULL);
           gtk_box_pack_start (GTK_BOX (hbox), dial, FALSE, FALSE, 0);
           gtk_widget_show (dial);