ENH: deprecate itk::IsSame and the header which implements it

It should be replaced by std::is_same from STL.

Documentation/ITK5MigrationGuide.md

@@ -80,6 +80,7 @@ To modernize your code base, replace:
   * `FastMutexLock` with `std::mutex`, and `#include "itkFastMutexLock.h"`  with `#include <mutex>`.
   * `MutexLock` with `std::mutex`, and `#include "itkMutexLock.h"`  with `#include <mutex>`.
   * `mpl::EnableIf<X>::Type` with `std::enable_if_t<X>`, and `#include "itkEnableIf.h"` with `#include <type_traits>`.
+  * `mpl::IsSame<X, Y>::Value` with `std::is_same<X, Y>::value`, and `#include "itkIsSame.h"` with `#include <type_traits>`.
 
 
 Modern CMake requirement

Modules/Core/Common/include/itkIsSame.h

@@ -18,7 +18,11 @@
 #ifndef itkIsSame_h
 #define itkIsSame_h
 
-#include "itkMetaProgrammingLibrary.h"
+#include "itkMacro.h"
+
+#if !defined(ITK_LEGACY_REMOVE)
+
+#  include "itkMetaProgrammingLibrary.h"
 
 namespace itk
 {
@@ -50,4 +54,8 @@ using mpl::IsSame;
 
 } // end namespace itk
 
+#else // ITK_LEGACY_REMOVE
+#  error Use C++ 11 std::is_same directly
+#endif
+
 #endif // itkIsSame_h

Utilities/Maintenance/BuildHeaderTest.py

@@ -49,6 +49,7 @@
         "vtkCaptureScreen.h",  # these includes require VTK
         "itkMultiThreader.h",  # Compatibility file, it should not be used
         "itkEnableIf.h", # Compatibility file, it should not be used
+        "itkIsSame.h", # Compatibility file, it should not be used
         "itkViewImage.h",  # Depends on VTK_RENDERING_BACKEND
         "QuickView.h",  # Depends on VTK_RENDERING_BACKEND
         "itkBSplineDeformableTransformInitializer.h",