BUG: Common naming of \#define conflicts with ITK

When VTK and ITK are used together, the
\#define ThreadInfoStruct vtkMultiThreader::ThreadInfo
from VTK/Common/Core/vtkMultiThreader.h

would clobber the ThreadInfoStruct definition from
ITK/Modules/Core/Common/include/itkMultiThreaderBase.h:
104   struct ThreadInfoStruct
105     {
106     ThreadIdType ThreadID;
107     ThreadIdType NumberOfThreads;
108     void* UserData;
109     ThreadFunctionType ThreadFunction;
110     enum { SUCCESS, ITK_EXCEPTION, ITK_PROCESS_ABORTED_EXCEPTION, STD_EXCEPTION, UNKNOWN } ThreadExitCode;
111     };

=====
using ThreadInfoStruct=vtkMultiThreader::ThreadInfo;

avoids the pre-processor conflicts.

=====

See https://discourse.itk.org/t/vtk9-and-itk5-conflicts/802
for discussion.

Author: hjmjohnson

Common/Core/vtkMultiThreader.h

@@ -94,8 +94,6 @@ class VTKCOMMONCORE_EXPORT vtkMultiThreader : public vtkObject
    * The UserData is the (void *)arg passed into the SetSingleMethod,
    * SetMultipleMethod, or SpawnThread method.
    */
-
-#define ThreadInfoStruct vtkMultiThreader::ThreadInfo
   class ThreadInfo
   {
   public:
@@ -228,5 +226,7 @@ class VTKCOMMONCORE_EXPORT vtkMultiThreader : public vtkObject
   void operator=(const vtkMultiThreader&) = delete;
 };
 
+using ThreadInfoStruct=vtkMultiThreader::ThreadInfo;
+
 #endif