Adding C-Python compatible API for embedding GraalPy

[lokmeinmatz]

This is a WIP as outcome from a project seminar at HPI, supervised by @timfel

Main idea is:

• generate a new dylib from the com.oracle.graal.python.c_embed Cmake project
• link against pythonnative lib from "cext" as well as "pythonvm" lib from graalpy itself
• c_embed handles
  • creating graal isolate
  • calling to graalpy so it can set Builtins, create PythonLanguage context etc.
  • taking the GIL because this is how C-python behaves
• Cleanup (not implemented yet)

The rest of the API calls are made to the methods in cext (works because everything is in flat namespace when linked together)

The example embedding was developed using Rust & pyo3. https://github.com/lokmeinmatz/pyo3/tree/graalpy_impl

in Folder examples/basic_rust_to_py is an example that is configured to work with GraalPy (may need some extra config to link on other OS than OSX)

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