EnsightCombinedReader: Improve tetrahedron cells reading

This MR supercedes vtk/vtk!11553 (closed)

This MR improves performances of the new vtkEnSightGoldCombinedReader in various ways, especially when reading large binary files containing nfaced/tetrahedron cells:

• The tetrahedron cell-building logic used a non-tetrahedron-specific vtkUnstructredGrid::InsertNextCell call which performed poorly due to a large amount of time spent managing a std::set, and struggling with memory allocation previsions.
• Read tetrahedron cells connectivity data as one block rather than cell-by-cell
• Added new "skip" methods to vtkEnSightDataSet which implement dedicated logic to ignore file cell sections. The logic is duplicated a bit from the equivalent reading methods at the benefit of much faster parsing during the RequestInfo pass (to get the parts names)
• Fixed a int overflow that could occur while seeking ahead in large files