Don't override col_cls in DynamicTable.add_column

[rly]

Motivation

Issue: If a user extends DynamicTableRegion or EnumData and tries to create a column with that subclass, using the table or enum keyword args, their subclass argument gets replaced with the base DynamicTableRegion or EnumData classes.
Solution: Use the passed col_cls. If not provided, then use the base DynamicTableRegion or EnumData classes.

TODO: Add a quick test

Checklist

• Did you update CHANGELOG.md with your changes?
• Does the PR clearly describe the problem and the solution?
• Have you reviewed our Contributing Guide?
• Does the PR use "Fix #XXX" notation to tell GitHub to close the relevant issue numbered XXX when the PR is merged?

[mavaylon1]

Will this be in by next milestone?

[VisLab]

Please let us know when it gets in. We are relying on it for implementation of ndx-hed.

[codecov]

Codecov Report

Attention: Patch coverage is 92.85714% with 1 line in your changes missing coverage. Please review.

Project coverage is 87.00%. Comparing base (775fa3b) to head (b4f33ef).

Files with missing lines	Patch %	Lines
src/hdmf/common/table.py	92.30%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1091      +/-   ##
==========================================
- Coverage   87.18%   87.00%   -0.18%     
==========================================
  Files          42       42              
  Lines        9532     9537       +5     
  Branches     1922     1926       +4     
==========================================
- Hits         8310     8298      -12     
- Misses        908      918      +10     
- Partials      314      321       +7     

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