HDF5: Handle unknown datatypes in datasets #2315

Job	Run time
clang7_nopy_nompi_h5_libcpp	25m 31s
clang7_nopy_ompi_h5_ad2_libcpp	15m 32s
clang7_nopy_ompi_h5_ad2_newLayout	19m 13s
clang14_py311_nompi_h5_ad2	19m 44s
clang8_py38_mpich_h5_ad2_newLayout	20m 39s
conda_ompi_all	12m 23s
gcc7_py36_pd_dd_ompi_h5_ad2	17m 57s
gcc9_py38_pd_nompi_h5_ad2_libcpp	11m 32s
musllinux_py10	9m 13s
	2h 31m 44s

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