Add type hints in the public API

[texasaggie97-zz]

• This contribution adheres to CONTRIBUTING.md.
• I've updated CHANGELOG.md if applicable.
• I've added tests applicable for this pull request

What does this Pull Request accomplish?

• Add type hints to public API
  • Uses type_in_documentation metadata since it mostly has the information needed - we need the complete list of possible types in the API, not just the type that is passed into the DLL
  • Several special cases to deal with free form test
  • Not sure how to put this information into the metadata
• Most type hints are calculated
• A few in fancy functions are hardcoded
• The preferred method for type hinting namedtuples is to create a class that inherits from typing.NamedTuple. This would require the couple of namedtuples we have to be moved to custom types. I did not do that work for this PR.

List issues fixed by this Pull Request below, if any.

What testing has been done?

• Unit tests and flake8 still pass with type hinting added
• Need to add mypy tests, maybe using examples?

[codecov]

Codecov Report

Merging #1530 (28c9e39) into master (be1d5aa) will decrease coverage by 0.33%.
The diff coverage is 87.32%.

@@            Coverage Diff             @@
##           master    #1530      +/-   ##
==========================================
- Coverage   91.66%   91.33%   -0.34%     
==========================================
  Files          20       20              
  Lines        3457     3510      +53     
==========================================
+ Hits         3169     3206      +37     
- Misses        288      304      +16     

Flag	Coverage Δ
codegenunittests	87.75% <64.70%> (-0.52%)	⬇️
nifakeunittests	96.35% <100.00%> (+<0.01%)	⬆️
nimodinstunittests	95.40% <100.00%> (+0.02%)	⬆️
nitclkunittests	95.65% <100.00%> (+0.03%)	⬆️

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Impacted Files	Coverage Δ
build/helper/codegen_helper.py	90.22% <7.69%> (-2.30%)	⬇️
build/helper/metadata_add_all.py	81.85% <83.78%> (+0.50%)	⬆️
build/helper/__init__.py	100.00% <100.00%> (ø)
generated/nifake/nifake/session.py	97.71% <100.00%> (+<0.01%)	⬆️
generated/nimodinst/nimodinst/session.py	95.40% <100.00%> (+0.02%)	⬆️
generated/nitclk/nitclk/session.py	95.65% <100.00%> (+0.03%)	⬆️

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