Menno Deij - van Rijswijk authored May 28, 2021 and Cory Quammen committed Oct 26, 2021

For scenarios with vtkMappedUnstructuredGrid input, the vtkPlaneCutter algorithm has been changed to accept input of type vtkUnstructuredGridBase.

* Refactored out mapped unstructured grid generation into new module Testing/DataModel
* Refactored existing tests that use mapped unstructured grid, remove code duplication
* Added test for vtkPlaneCutter on mapped unstructured grid.
* Modified vtkMappedUnstructuredGrid requirements and implementation
  - void GetFaceStream(vtkIdType cellId, vtkIdList* ptIds) is now required to be
    implemented by an implementation used by vtkMappedUnstructuredGrid
  - added call to this for cells that require explicit face representation
* Updated vtkCPExodusIIElementBlock implemenation with GetFaceStream
  - method is there, but issues a not-implemented error.