TechDraw: fix leader positioning (snapping) (#24468)

* [TD]specialize leader snap handling

* [TD]fix leader live update regression

* [TD]QGTracker code clean-up

src/Mod/TechDraw/App/DrawLeaderLine.h

@@ -93,6 +93,8 @@ public:
 
     Base::Vector3d lastSegmentDirection() const;
 
+    bool snapsToPosition() const override { return false; }
+
 private:
 
 

src/Mod/TechDraw/App/DrawView.h

@@ -127,6 +127,8 @@ public:
 
     static bool isProjGroupItem(DrawViewPart* item);
 
+    virtual bool snapsToPosition() const { return true; }
+
 protected:
     void onBeforeChange(const App::Property *prop) override;
     void onChanged(const App::Property* prop) override;