VTKWriter: the index type should be explicitly std::int32_t, not int

namespace details {

// TODO: 64-bit integers are most likely not supported in the BINARY format

// legacy VTK files do not support 64-bit integers, even in the BINARY format

inline void

writeInt( VTK::FileFormat format, std::ostream& str, int value )

writeInt( VTK::FileFormat format, std::ostream& str, std::int32_t value )

{

   if( format == VTK::FileFormat::binary ) {

      value = forceBigEndian( value );

      str.write( reinterpret_cast<const char*>(&value), sizeof(int) );

      str.write( reinterpret_cast<const char*>(&value), sizeof(std::int32_t) );

   }

   else {

      str << value << " ";