Change: Hide bevel for resizeable sparse layout windows. (#11572)

When clicked, the button is still highlighted to show that it is active.

The bevel is controlled with widget_data by RWV_SHOW_BEVEL or RWV_HIDE_BEVEL values.

src/widget_type.h

@@ -36,6 +36,12 @@ enum ArrowWidgetValues {
 	AWV_RIGHT,    ///< Force the arrow to the right
 };
 
+/** WidgetData values for a resize box widget. */
+enum ResizeWidgetValues {
+	RWV_SHOW_BEVEL, ///< Bevel of resize box is shown.
+	RWV_HIDE_BEVEL, ///< Bevel of resize box is hidden.
+};
+
 /**
  * Window widget types, nested widget types, and nested widget part types.
  */