STYLE: Replace itkStaticConstMacro with static constexpr

Use static constexpr directly now that C++11 conformance
is required by all compilers.

:%s/itkStaticConstMacro *( *\([^,]*\),[ \_s]*\([^,]*\),\_s*\([^)]*\)) */static constexpr \2 \1 = \3/ge

'itkStaticConstMacro(name, type, value)' became unconditionally
identical to 'static constexpr type name = value' with ITK commit
aec95193ab00e1322039911e1032da00f3a103b6 "ENH: Update compiler macros (#810)",
maekclena, 7 May 2019.

'itkGetStaticConstMacro(name)' became unconditionally identical to
'(Self::name)' with ITK commit 84e490b81e3f3c2b0edb89ae7b9de53bfc52f2b2
"Removing some outdated compiler conditionals", Hans Johnson, 31 July
2010.

Most 'itkStaticConstMacro' calls were removed by ITK commit 5c14741e1e063a132ea7e7ee69c5bd0a4e49af74

Author: hjmjohnson

include/itkPhysicalCentralDifferenceImageFunction.h

@@ -52,7 +52,7 @@ class ITK_TEMPLATE_EXPORT PhysicalCentralDifferenceImageFunction
   /** Standard class type alias. */
   using Self = PhysicalCentralDifferenceImageFunction;
   using Superclass =
-    ImageFunction<TInputImage, CovariantVector<double, itkGetStaticConstMacro(ImageDimension)>, TCoordRep>;
+    ImageFunction<TInputImage, CovariantVector<double, Self::ImageDimension>, TCoordRep>;
   using Pointer = SmartPointer<Self>;
   using ConstPointer = SmartPointer<const Self>;