Set fixed values and column attrs on autogen class

[rly]

Motivation

Fix #798

How to test the behavior?

Show how to reproduce the new behavior (can be a bug fix or a new feature)

Checklist

• Did you update CHANGELOG.md with your changes?
• Have you checked our Contributing document?
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[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (afd1882) 88.57% compared to head (1d68452) 88.59%.
Report is 1 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #800      +/-   ##
==========================================
+ Coverage   88.57%   88.59%   +0.01%     
==========================================
  Files          45       45              
  Lines        9400     9424      +24     
  Branches     2673     2684      +11     
==========================================
+ Hits         8326     8349      +23     
- Misses        759      760       +1     
  Partials      315      315              

Files	Coverage Δ
src/hdmf/build/classgenerator.py	95.41% <100.00%> (+0.43%)	⬆️
src/hdmf/common/table.py	86.38% <100.00%> (+0.44%)	⬆️
src/hdmf/spec/spec.py	90.89% <100.00%> (+0.03%)	⬆️
src/hdmf/common/io/table.py	75.00% <85.71%> (-8.84%)	⬇️

... and 1 file with indirect coverage changes

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[rly]

This issue is blocking progress on the ndx-events extension and also I should have been finished it a long time ago...

[rly]

Also fix #972.

[rly]

Also fix #973 which uses related code.