0026195: Visualization - optimize selection algorithms

- initial transformation of triangulation is now applied to selecting frustum;
- switched from NCollection_Vec3 to gp collections to avoid conversions and usage of macros;
- calculation of frustum was refactored to reduce its build time;
- double pixel tolerances for selection were replaced by integer ones;
- switched to splitting along the main axis only in SelectMgr BVH selection primitive sets.

src/gp/gp_XYZ.hxx

@@ -80,6 +80,16 @@ public:
     Standard_Real& ChangeCoord (const Standard_Integer theIndex);
   
     void Coord (Standard_Real& X, Standard_Real& Y, Standard_Real& Z) const;
+
+    //! Returns a const ptr to coordinates location.
+    //! Is useful for algorithms, but DOES NOT PERFORM
+    //! ANY CHECKS!
+    inline const Standard_Real* GetData() const { return (&x); }
+
+    //! Returns a ptr to coordinates location.
+    //! Is useful for algorithms, but DOES NOT PERFORM
+    //! ANY CHECKS!
+    inline Standard_Real* ChangeData() { return (&x); }
   
   //! Returns the X coordinate
     Standard_Real X() const;