BUG: Revert declare-then-init where it changes copy/move semantics

Fix three cases where merging declaration and assignment changed the
operation being tested:

- itkImageRegionConstIteratorWithOnlyIndexTest.cxx: index captured
  before GoToBegin() read past-the-end position instead of begin
- itkRangeGTestUtilities.h: copy/move-assign tests now exercise
  constructors instead of assignment operators
- itkImageIteratorTest.cxx: assignment operator test invoked copy
  constructor instead

Found by Greptile code review (1 P1, 2 P2).

Author: hjmjohnson

Modules/Core/Common/test/itkImageIteratorTest.cxx

@@ -97,7 +97,8 @@ itkImageIteratorTest(int, char *[])
   const VectorImageIterator itr3(itr1);
 
   // Exercise assignment operator
-  const VectorImageIterator itr4 = itr1;
+  VectorImageIterator itr4;
+  itr4 = itr1;
 
   // Exercise operator!=
   if (itr4 != itr1)

Modules/Core/Common/test/itkImageRegionConstIteratorWithOnlyIndexTest.cxx

@@ -122,8 +122,8 @@ class itkImageRegionConstIteratorWithOnlyIndexTestIteratorTester
     }
 
     // Test iterating fwd by line
-    IndexType index = it.GetIndex();
     it.GoToBegin();
+    IndexType index = it.GetIndex();
     for (unsigned int i = 0; i < region.GetSize()[0]; ++i)
     {
       ++it;

Modules/Core/Common/test/itkRangeGTestUtilities.h

@@ -82,7 +82,8 @@ class RangeGTestUtilities
   static void
   ExpectCopyAssignedRangeHasSameIteratorsAsOriginal(const TRange & originalRange)
   {
-    TRange copyAssignedRange = originalRange;
+    TRange copyAssignedRange;
+    copyAssignedRange = originalRange;
 
     ExpectRangesHaveEqualBeginAndEnd(copyAssignedRange, originalRange);
   }
@@ -105,7 +106,8 @@ class RangeGTestUtilities
   {
     const TRange originalRangeBeforeMove = originalRange;
 
-    TRange moveAssignedRange = std::move(originalRange);
+    TRange moveAssignedRange;
+    moveAssignedRange = std::move(originalRange);
 
     ExpectRangesHaveEqualBeginAndEnd(moveAssignedRange, originalRangeBeforeMove);
   }