remove autodetection of dtype from HDF5IO

[ajtritt]

Problem/Use Case

HDF5IO has logic for automatically determining dtype. This leads to the risk of different dtype serialization for different backends. To avoid this, dtype should be detected in ObjectMapper and passed into FORMIO/HDF5IO through DatasetBuilder.

• Add dtype detection to ObjectMapper
• Establish keys that Builders accept and which FORMIO also understands. The keys currently located at HDF5IO.__dtypes will probably suffice, but they should be explicitly established as allowable keys in DatasetBuilder.
• Remove HDF5IO.get_type

Checklist

• Have you ensured the feature or change was not already reported ?
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• Have you included a clear description of the problem you are trying to solve?
• Have you included a minimal code snippet that reproduces the issue you are encountering?