CGAL Lab: Transformation of point normals (#7935)

## Summary of Changes

Affine transformation transforms points, but didn't transform their
normals. This PR takes care of normal transformation of point sets.

## Release Management

* Affected package(s): Polyhedron Demo

Polyhedron/demo/Polyhedron/Plugins/PCA/Affine_transform_plugin.cpp

@@ -614,12 +614,20 @@ endPointSet(const QMatrix4x4& transform_matrix)
   Point_set* new_ps = new_item->point_set();
   CGAL::qglviewer::Vec c = aff_transformed_item->center();
 
+  QMatrix3x3 normal_matrix = transform_matrix.normalMatrix();
+
   for(Point_set::Index idx : *new_ps)
   {
     QVector3D vec = transform_matrix.map(QVector3D(new_ps->point(idx).x() - c.x,
                                                    new_ps->point(idx).y() - c.y,
                                                    new_ps->point(idx).z() - c.z));
     new_ps->point(idx) = Kernel::Point_3(vec.x(), vec.y(), vec.z());
+    if (new_ps->has_normal_map()) {
+      QVector3D n(new_ps->normal(idx).x(), new_ps->normal(idx).y(), new_ps->normal(idx).z());
+      new_ps->normal(idx) = Kernel::Vector_3(normal_matrix(0, 0) * n[0] + normal_matrix(0, 1) * n[1] + normal_matrix(0, 2) * n[2],
+                                             normal_matrix(1, 0) * n[0] + normal_matrix(1, 1) * n[1] + normal_matrix(1, 2) * n[2],
+                                             normal_matrix(2, 0) * n[0] + normal_matrix(2, 1) * n[1] + normal_matrix(2, 2) * n[2]);
+    }
   }
 
   new_item->setName(aff_transformed_item->name());