Support for argument names, keyword arguments and argument default values

[melven]

Inspired by pybind11, this allows to write:

m.method("name", &function, jlcxx::arg("firstArg"), jlcxx::arg("secondArg")=7, jlcxx::kwarg("hello")=5, jlcxx::kwarg("there")=42);

Which translates roughly to:

name(firstArg::Type1, secondArg::Type2 = 7; hello::Type3, there::Type4 = 42)

Also supports docstrings (just a const char* argument) and additional arguments of some variants of method (calling convention) have extra enum types (to allow parsing arbitrary arguments).
Example:

  mod.method("test_exception", test_exception, jlcxx::calling_policy::std_function);

[melven]

Needs again corresponding changes in libcxxwrap-julia: JuliaInterop/libcxxwrap-julia#142

Is based on the docstring merge request #396 ...

[barche]

Thanks for this, I would like to integrate this together with the docstring support in the next release, so that way we only have one breaking change.

[barche]

If this is ready for you I can merge this into the testjll branch before merging JuliaInterop/libcxxwrap-julia#142 so everything is tested.

[melven]

Ready from my side - only remaining thing is to further update the README (breaking changes and examples for keyword/default arguments)

[barche]

It seems that sometimes an extra \0 is added to the method symbols:

Expression: ((methods(CppTestFunctions.concatenate_numbers_with_named_args))[1]).slot_syms == "#self#\0i\0d\0val\0"
    Evaluated: "#self#\0i\0d\0val\0\0" == "#self#\0i\0d\0val\0"

See log at e.g. https://github.com/JuliaInterop/libcxxwrap-julia/actions/runs/7514928755/job/20458329641#step:4:495

And there is also a precompile error on Julia 1.6:
https://github.com/JuliaInterop/libcxxwrap-julia/actions/runs/7514928755/job/20458329374#step:4:343

[melven]

I tried to fix both problems, can you triger the checks @barche ?

[barche]

Thanks, I added your last commit to the testjll branch and did one more small fix, and now all tests pass. I'll rebuild a JLL now on Yggdrasil, and then manually merge this from testjll to main.

[barche]

The changes are merged into main now, it should be possible to test by doing add CxxWrap#main.