bpo-35239: _PySys_EndInit() copies module_search_path (GH-10532)

* The _PySys_EndInit() function now copies the
  config->module_search_path list, so config is longer modified when
  sys.path is updated.
* config->warnoptions list and config->xoptions dict are also copied
* test_embed: InitConfigTests now also tests
  main_config['module_search_path']
* Fix _Py_InitializeMainInterpreter(): don't use config->warnoptions
   but sys.warnoptions to decide if the warnings module should
   be imported at startup.