Missing fields for loaded extension types that extend other extension types

[rly]

Description

See rly/ndx-events#3 . This probably has to do with the fact that both Events and LabeledEvents are defined in ndx-events, and LabeledEvents extends Events, but needs to be investigated further.

Environment

Python Executable: Conda
Python Version: Python 3.8
Operating System: Windows
HDMF Version: 2.3.0

Checklist

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