nodeview: implemented dragger to create edge without holding key

app/widget/nodeview/nodeviewitem.h

@@ -125,6 +125,11 @@ public:
     return prevent_removing_;
   }
 
+  const QPolygonF &GetOutputTriangle() const
+  {
+    return output_triangle_;
+  }
+
 protected:
   virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget = nullptr) override;
 
@@ -190,6 +195,8 @@ private:
 
   bool prevent_removing_;
 
+  QPolygonF output_triangle_;
+
 };
 
 }