By introducing our own custom thrust execution policy we can make sure
to hit the fastest code paths in thrust for the sort operation. This makes
sure that for UInt32,Int32, and Float32 we use the radix sort from thrust
which offers a 2x to 3x speed improvement over the merge sort implementation.

Secondly by telling thrust that our BinaryOperators are commutative we
make sure that we get the fastest code paths when executing Inclusive
and Exclusive Scan

Benchmark 'Radix Sort on 1048576 random values vtkm::Int32' results:
  median = 0.0117049s
  median abs dev = 0.00324614s
  mean = 0.0167615s
  std dev = 0.00786269s
  min = 0.00845875s
  max = 0.0389063s
Benchmark 'Radix Sort on 1048576 random values vtkm::Float32' results:
  median = 0.0234463s
  median abs dev = 0.000317249s
  mean = 0.021452s
  std dev = 0.00470307s
  min = 0.011255s
  max = 0.0250643s
Benchmark 'Merge Sort on 1048576 random values vtkm::Int32' results:
  median = 0.0310486s
  median abs dev = 0.000182129s
  mean = 0.0286914s
  std dev = 0.00634102s
  min = 0.0116225s
  max = 0.0317379s
Benchmark 'Merge Sort on 1048576 random values vtkm::Float32' results:
  median = 0.0310617s
  median abs dev = 0.000193583s
  mean = 0.0295779s
  std dev = 0.00491531s
  min = 0.0147257s
  max = 0.032307s