bpo-32030: Add _PyCoreConfig.module_search_paths (#4954)

_PyCoreConfig_Read() is now responsible to compute sys.path.
So sys.path is now computed before calling _Py_InitializeCore().

Changes:

* Add module_search_path, module_search_paths, executable, prefix,
  base_prefix, exec_prefix and base_exec_prefix to _PyCoreConfig.
* _PyMainInterpreterConfig_Read() now only converts wchar_t** lists
  into a Python list, it doesn't compute sys.path anymore.