Extended dataset can be written with invalid data type

[rly]

Description

See #609 (comment)

In PyNWB, the "electrodes" table has neurodata_type DynamicTable and is a subgroup of the neurodata_type "NWBFile". It, like other tables, specifies specific VectorData type columns that are not part of the original DynamicTable spec, such as a column for "filtering" that has dtype float. This dtype is not currently used in the building/writing process, so the "filtering" column could be written with a string dtype instead. (This was discovered because the dtype should be a string dtype. See NeurodataWithoutBorders/nwb-schema#478).

The build/write process should check that the dtype of the extended dataset being written is of the correct dtype or can be converted to the correct dtype prior to writing.

Environment

Python Executable: Conda
Python Version: Python 3.8
Operating System: Windows
HDMF Version: dev

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