bpo-36763: Add _PyCoreConfig.parse_argv (GH-13361)

* _PyCoreConfig_Read() doesn't parse nor update argv
  if parse_argv is 0.
* Move path configuration fields in _PyCoreConfig.
* Add an unit test for parse_argv=0.
* Remove unused "done": label in _Py_RunMain().

Modules/main.c

@@ -574,13 +574,13 @@ _Py_RunMain(void)
     int exitcode = 0;
 
     pymain_run_python(&exitcode);
+
     if (Py_FinalizeEx() < 0) {
         /* Value unlikely to be confused with a non-error exit status or
            other special meaning */
         exitcode = 120;
     }
 
-done:
     pymain_free();
 
     if (_Py_UnhandledKeyboardInterrupt) {