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"Removing some outdated compiler conditionals", Hans Johnson, 31 July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

documentation/Doxygen/doxygen.config.in

@@ -2106,7 +2106,7 @@ INCLUDE_FILE_PATTERNS  =
 # This tag requires that the tag ENABLE_PREPROCESSING is set to YES.
 
 PREDEFINED             = "itkNotUsed(x)=" \
-                         "itkStaticConstMacro(name,type,value)=static constexpr type name = value" \
+                         "static constexpr type name = value=static constexpr type name = value" \
                          "itkSetInputMacro(name, type, number)=                   virtual void Set##name##Input(const type *_arg);                   virtual void SetInput##number(const type *_arg);" \
                          "itkGetInputMacro(name, type, number)=                   virtual const type * Get##name##Input() const;                   virtual const type * GetInput##number() const;" \
                          "itkSetMacro(name,type)=                   virtual void Set##name (type _arg);" \