Getting rid of input ghost level parameter in diy ghost cell generator

This issue follows !7548 (merged). Currently, the diy based ghost cell generator (vtkGhostCellsGenerator) takes as input the number of ghost layers of the input set of data sets. This amount of ghost layers is then used to peel off ghosts from the input when generating them in the output. This peeling step is important because we have no guarantee on the uniformity of the inputs w.r.t. ghosts. This input paramter makes sense if every block in the input have the same number of ghost layers, but this is not enforced.

There is a way to not rely on this input parameter by doing an extensive sweeping of the input data sets one by one to determine the amount of ghost layers in each of them. This should be done in the function PeelOfGhostLayers in vtkDIYGhostUtilities.cxx.