fix: allow for stacked monitors in dirtomon

Stacking monitors vertically prevented dirtomon from
finding any adjacent monitor.

dwl.c

@@ -1318,7 +1318,7 @@ dirtomon(enum wlr_direction dir)
 		return next->data;
 	if (wlr_output_layout_get(output_layout, selmon->wlr_output)
 	    && (next = wlr_output_layout_farthest_output(output_layout,
-							 dir ^ (WLR_DIRECTION_LEFT|WLR_DIRECTION_RIGHT),
+							 dir ^ (WLR_DIRECTION_LEFT|WLR_DIRECTION_RIGHT|WLR_DIRECTION_UP|WLR_DIRECTION_DOWN),
 							 selmon->wlr_output, selmon->m.x, selmon->m.y)))
 		return next->data;
 	return selmon;