[TD]Fix section snapping (fix #15961) (#15450)

* [TD]Add view snapping preferences

* [TD]fix section snapping algo

- snap sections to section normal line.
- snap views to other views in X&Y

* [TD]fix snapping to ProjectionGroups

src/Mod/TechDraw/App/DrawView.h

@@ -40,7 +40,7 @@ class DrawPage;
 class DrawViewCollection;
 class DrawViewClip;
 class DrawLeaderLine;
-/*class CosmeticVertex;*/
+class DrawViewPart;
 
 /** Base class of all View Features in the drawing module
  */
@@ -123,6 +123,8 @@ public:
 
     virtual App::PropertyLink *getOwnerProperty() { return nullptr; }
 
+    static bool isProjGroupItem(DrawViewPart* item);
+
 protected:
     void onBeforeChange(const App::Property *prop) override;
     void onChanged(const App::Property* prop) override;