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

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.
(cherry picked from commit 37cd982df02795905886ab36a2378ed557cb6f60)

Co-authored-by: Victor Stinner <vstinner@redhat.com>