ENH: Remove getHDF5Type from XdmfArray and move into XdmfHDF5Writer so all hdf5 interaction is isolated
in XdmfHDF5Writer.  Friend the XdmfHDF5Writer from XdmfArray so that it can access the variant to perform
typesafe operations on the data stored.  Variable macro generation didn't work so reverted the modified code.
We may just have to write ugly static New() methods when required.