Workflow generator supports abstract classes

[WhitWaldo]

Description

Fixing reported issue with abstract workflows not properly generating. Proactively went and added other tests to validate correctness:

• Abstract open (C# 15 feature) classes
• Concrete open (again, C# 15 feature) classes
• Abstract generic base class
• Abstract open generic class
• Concrete open generic class
• Concrete closed (workflow versioning)
• Non-workflow class (validate no workflows registered) - false-positive guard

Issue reference

We strive to have all PR being opened based on an issue, where the problem or feature have been discussed prior to implementation.

Please reference the issue this PR will close: #1898

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.61%. Comparing base (1c24788) to head (9b4e4b2).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1902      +/-   ##
==========================================
- Coverage   62.62%   62.61%   -0.02%     
==========================================
  Files         338      338              
  Lines        9972     9972              
  Branches     1174     1174              
==========================================
- Hits         6245     6244       -1     
  Misses       3403     3403              
- Partials      324      325       +1     

Flag	Coverage Δ
net10.0	62.57% <ø> (-0.02%)	⬇️

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