Re-add support for reading cell and vertex solution in CGNS Reader
With ParaView 5.4, when reading a steady CGNS solution file (without FlowSolutionPointers), only first FlowSolution_t node is read. Previously, the first FlowSolution_t on Vertex and the first FlowSolution_t on CellCenter were read. Thus, the new behavior is not coherent with the GUI where the user can still select both variables at node and at cell location. The new behavior seems misleading.