COMP: Fix TransformPhysicalPointToIndex nodiscard warnings

When the `bool` return value of a `TransformPhysicalPointToIndex(point, index)`
call can be ignored, it is preferable (for performance reasons) to call the
`TransformPhysicalPointToIndex(point)` overload that just returns the index,
preventing `[[nodiscard]]` compile warnings.

These cases are found in Visual Studio, using the following regular expression:
`  [^ ]+->TransformPhysicalPointToIndex\(.*,`

Author: N-Dekker

Modules/Nonunit/Review/include/itkMultiphaseDenseFiniteDifferenceImageFilter.hxx

@@ -49,8 +49,7 @@ MultiphaseDenseFiniteDifferenceImageFilter<TInputImage, TFeatureImage, TOutputIm
 
     // Find the index of the target image where this Level Set
     // should be pasted.
-    OutputIndexType start;
-    output->TransformPhysicalPointToIndex(origin, start);
+    OutputIndexType start = output->TransformPhysicalPointToIndex(origin);
 
     OutputRegionType region;
     region.SetSize(size);

Modules/Nonunit/Review/include/itkMultiphaseSparseFiniteDifferenceImageFilter.hxx

@@ -1353,8 +1353,7 @@ MultiphaseSparseFiniteDifferenceImageFilter<TInputImage, TFeatureImage, TOutputI
     ImageRegionIterator<InputImageType> inIt(this->m_LevelSet[fId], this->m_LevelSet[fId]->GetRequestedRegion());
 
     // In the context of the global coordinates
-    OutputIndexType start;
-    output->TransformPhysicalPointToIndex(origin, start);
+    OutputIndexType start = output->TransformPhysicalPointToIndex(origin);
 
     // Defining sub-region in the global coordinates
     OutputRegionType region;

Modules/Nonunit/Review/include/itkRegionBasedLevelSetFunctionData.hxx

@@ -46,7 +46,7 @@ RegionBasedLevelSetFunctionData<TInputImage, TFeatureImage>::CreateHeavisideFunc
 
   const InputPointType origin = image->GetOrigin();
 
-  this->m_HeavisideFunctionOfLevelSetImage->TransformPhysicalPointToIndex(origin, this->m_Start);
+  this->m_Start = this->m_HeavisideFunctionOfLevelSetImage->TransformPhysicalPointToIndex(origin);
 
   for (unsigned int i = 0; i < ImageDimension; ++i)
   {

Modules/Nonunit/Review/include/itkScalarChanAndVeseDenseLevelSetImageFilter.hxx

@@ -33,8 +33,7 @@ ScalarChanAndVeseDenseLevelSetImageFilter<TInputImage, TFeatureImage, TOutputIma
     InputPointType    origin = input->GetOrigin();
 
     // In the context of the global coordinates
-    FeatureIndexType start;
-    this->GetInput()->TransformPhysicalPointToIndex(origin, start);
+    FeatureIndexType start = this->GetInput()->TransformPhysicalPointToIndex(origin);
 
     // Defining roi region
     FeatureRegionType region;

Modules/Nonunit/Review/include/itkScalarChanAndVeseSparseLevelSetImageFilter.hxx

@@ -38,8 +38,7 @@ ScalarChanAndVeseSparseLevelSetImageFilter<TInputImage, TFeatureImage, TOutputIm
     InputPointType    origin = input->GetOrigin();
 
     // In the context of the global coordinates
-    FeatureIndexType start;
-    this->GetInput()->TransformPhysicalPointToIndex(origin, start);
+    FeatureIndexType start = this->GetInput()->TransformPhysicalPointToIndex(origin);
 
     // Defining roi region
     FeatureRegionType region;

Modules/Registration/FEM/include/itkFEMFiniteDifferenceFunctionLoad.hxx

@@ -243,7 +243,7 @@ FiniteDifferenceFunctionLoad<TMoving, TFixed>::Fe(FEMVectorType Gpos) -> FEMVect
     physicalPoint[k] = Gpos[k];
   }
 
-  m_FixedImage->TransformPhysicalPointToIndex(physicalPoint, oindex);
+  oindex = m_FixedImage->TransformPhysicalPointToIndex(physicalPoint);
 
   for (unsigned int k = 0; k < ImageDimension; ++k)
   {

Modules/Registration/FEM/test/itkFEMFiniteDifferenceFunctionLoadTest.cxx

@@ -316,7 +316,7 @@ RunTest(InputImageType *            fixedImage,
       {
         coords[d] = element->GetNodeCoordinates(n)[d];
       }
-      fixedImage->TransformPhysicalPointToIndex(coords, index);
+      index = fixedImage->TransformPhysicalPointToIndex(coords);
       if (!region.IsInside(index))
       {
         continue;