vtkHDF : Support vtkPartitionedDataSetCollection and vtkMultiblockDataset in reader and writer

Implement partial support for composite types of datasets in vtkHDF writer and reader.

For full PDC/MB support in vtkHDF, this MR still misses :

• Writer : Actual support for vtkPartitionedDataSet. For now, we only write the first partition. Parallel writing is not supported
• Writer : composite + transient (may work as intended, but untested)
• Reader : composite + transient