fix(sankey): make label in the front of rect, recover the change of #14417.

src/chart/sankey/SankeyView.ts

@@ -250,7 +250,8 @@ class SankeyView extends ChartView {
                     width: layout.dx,
                     height: layout.dy
                 },
-                style: itemModel.getModel('itemStyle').getItemStyle()
+                style: itemModel.getModel('itemStyle').getItemStyle(),
+                z2: 10
             });
 
             setLabelStyle(