Merge all recent work on virtual geometry into main

Much recent work on virtual surfaces is included in this MR. Three concrete instances of GeoVSurfaceShape (GeoRectSurface, GeoTrapezoidSurface, and GeoAnnulusSurface) are now included. GeoVSurfaceShape is used with GeoVSurface following the pattern of LogVols and PhysVol. A new example plugin called SiliconSystemPlugin demonstrates the use of these classes.

GeoModelCore/GeoModelKernel/GeoModelKernel/GeoAccessSurfaceAction.h

+/*
+  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
+*/
+
+#ifndef GeoAccessSurfaceAction_h
+#define GeoAccessSurfaceAction_h 1
+
+#include "GeoModelKernel/GeoNodeAction.h"
+#include "GeoModelKernel/GeoDefinitions.h"
+#include <vector>
+
+class GeoVSurface;
+class GeoVPhysVol;
+class GeoTransform;
+class GeoVAlignmentStore;
+using VSConstLink = GeoIntrusivePtr<const GeoVSurface>;
+/**
+ * @class GeoAccessSurfaceAction
+ *
+ * @brief Accesses virtual surfaces, returning the ith surface and also its transformation relative to the parent.
+ */
+
+class GeoAccessSurfaceAction final : public GeoNodeAction
+{
+ public:
+  GeoAccessSurfaceAction (unsigned int Index, const GeoVAlignmentStore* store);
+  virtual ~GeoAccessSurfaceAction() override;
+
+  /// Handles a Transform.
+  virtual void handleTransform (const GeoTransform *xform) override;
+  
+  /// Handles a physical volume, to refresh the pendingTransformlist
+  virtual void handlePhysVol (const GeoPhysVol *vol) override;
+  
+  /// Handles a full physical volume, to refresh the pendingTransformlist
+  virtual void handleFullPhysVol (const GeoFullPhysVol *vol) override;  
+  
+  /// Handles a virtual surface.
+  virtual void handleVSurface (const GeoVSurface *surface) override;
+
+  /// Returns the selected virtual surface or nullptr if not found.
+  VSConstLink getSurface () const;
+
+  /// Returns the transformation to the surface.
+  const GeoTrf::Transform3D & getTransform () const;
+
+  /// Returns the default ransformation to the surface.
+  const GeoTrf::Transform3D & getDefTransform () const;
+
+ private:
+
+  GeoAccessSurfaceAction(const GeoAccessSurfaceAction &right);
+  GeoAccessSurfaceAction & operator=(const GeoAccessSurfaceAction &right);
+
+  /// Returns a pointer to the ith virtual surface under this one.
+  VSConstLink m_surface{};
+
+  /// The transformation to the ith surface.
+  GeoTrf::Transform3D m_transform{GeoTrf::Transform3D::Identity()};
+
+  /// The default transformation to the ith surface.
+  GeoTrf::Transform3D m_defTransform{GeoTrf::Transform3D::Identity()};
+
+  /// The surface which we are interested in seeking.
+  unsigned int m_index{0};
+
+  /// The surface which we are interested in seeking.
+  unsigned int m_counter{0};
+
+  /// List of Pending Transformations.
+  std::vector<const GeoTransform *>  m_pendingTransformList{};
+
+  const GeoVAlignmentStore* m_alignStore{nullptr};
+};
+
+#endif