Fix BufferID.placeholder static property, Doxygen docs

[parker-research]

During the M.CSS documentation generation setup, it errored when it got to the following:

        .def_property_readonly_static("placeholder", &BufferID::getPlaceholder)

The issue is that the static function is actually treated as a @classmethod in Python, and the associated C++ function is called with the cls = type(self) argument. In the fix, an anonymous function is used to discard the cls in the call.

Also added a note about Doxygen.in which I wish was present from the start.

[parker-research]

This bug is also mentioned in MikePopoloski/pyslang#96 - it caused a roadblock when someone struggled to generate type stubs.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.67%. Comparing base (0d48fb9) to head (e5e41aa).
Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1184   +/-   ##
=======================================
  Coverage   94.67%   94.67%           
=======================================
  Files         201      201           
  Lines       50552    50552           
=======================================
  Hits        47859    47859           
  Misses       2693     2693           

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0d48fb9...e5e41aa. Read the comment docs.

[Esser50K]

So pparently been fixed? how can I generate things now?

I tried using the nightly build but the issue mentioned on MikePopoloski/pyslang#96 is still present

[parker-research]

Just confirmed that as of pyslang commit a864e10 (which bumped the submodule version), both of the following work:

pip install mypy
stubgen -p pyslang

pip install pybind11-stubgen
pybind11-stubgen pyslang
# Note: Lots of error log messages. Generation still succeeds though.