Add a vtkProbeFilter SMP path for source image
The vtkProbeFilter already has an SMP-accelerated fast path for when the "Input" is a vtkImageData. The purpose of this MR is to add a new fast path for when the "Source" is a vtkImageData. This new fast path benefits from the use of SMP, and also from the simplicity of interpolating images as compared to interpolating abstract geometries.