COMP: Include the loss normalization where the metric threader uses it

The threader header named itk::Impact::LossNormalization without its
header, so it compiled only after another header had included it, which
the header test's order did not do.

Author: vboussot

include/itkImpactImageToImageMetricv4GetValueAndDerivativeThreader.h

@@ -21,6 +21,7 @@
 
 #include <itkImageToImageMetricv4GetValueAndDerivativeThreader.h>
 #include "ImpactLoss.h"
+#include "itkImpactLossNormalization.h"
 #include <algorithm>
 #include <random>