STYLE: Prefer = default to explicitly trivial implementations

This check replaces default bodies of special member functions with
= default;. The explicitly defaulted function declarations enable more
opportunities in optimization, because the compiler might treat
explicitly defaulted functions as trivial.

Additionally, the C++11 use of = default more clearly expreses the
intent for the special member functions.

Author: hjmjohnson

include/itkCoocurrenceTextureFeaturesImageFilter.h

@@ -214,7 +214,7 @@ class ITK_TEMPLATE_EXPORT CoocurrenceTextureFeaturesImageFilter : public ImageTo
   using NeighborIndexType = typename NeighborhoodIteratorType::NeighborIndexType;
 
   CoocurrenceTextureFeaturesImageFilter();
-  ~CoocurrenceTextureFeaturesImageFilter() override {}
+  ~CoocurrenceTextureFeaturesImageFilter() override = default;
 
   bool
   IsInsideNeighborhood(const OffsetType & iteratedOffset);

include/itkDigitizerFunctor.h

@@ -47,7 +47,7 @@ class Digitizer
     , m_Max(max)
   {}
 
-  ~Digitizer() {}
+  ~Digitizer() = default;
 
   bool
   operator!=(const Digitizer & other) const

include/itkFirstOrderTextureFeaturesImageFilter.h

@@ -96,7 +96,7 @@ class ITK_TEMPLATE_EXPORT FirstOrderTextureFeaturesImageFilter
     return 8;
   }
 
-  FirstOrderTextureFeaturesImageFilter() {}
+  FirstOrderTextureFeaturesImageFilter() = default;
 
   void
   GenerateOutputInformation() override
@@ -118,7 +118,7 @@ class ITK_TEMPLATE_EXPORT FirstOrderTextureFeaturesImageFilter
   }
 
 
-  ~FirstOrderTextureFeaturesImageFilter() override {}
+  ~FirstOrderTextureFeaturesImageFilter() override = default;
 };
 } // end namespace itk
 

include/itkRunLengthTextureFeaturesImageFilter.h

@@ -238,7 +238,7 @@ class ITK_TEMPLATE_EXPORT RunLengthTextureFeaturesImageFilter : public ImageToIm
   using NeighborIndexType = typename NeighborhoodIteratorType::NeighborIndexType;
 
   RunLengthTextureFeaturesImageFilter();
-  ~RunLengthTextureFeaturesImageFilter() override {}
+  ~RunLengthTextureFeaturesImageFilter() override = default;
 
   void
   NormalizeOffsetDirection(OffsetType & offset);