bpo-32030: Add _PyMainInterpreterConfig.program_name (#4548)

* Py_Main() now calls Py_SetProgramName() earlier to be able to get
  the program name in _PyMainInterpreterConfig_ReadEnv().
* Rename prog to program_name
* Rename progpath to program_name
diff --git a/Include/pystate.h b/Include/pystate.h
index 533851f..60d001c 100644
--- a/Include/pystate.h
+++ b/Include/pystate.h
@@ -64,6 +64,8 @@
     wchar_t *module_search_path_env;
     /* PYTHONHOME environment variable, see also Py_SetPythonHome(). */
     wchar_t *home;
+    /* Program name, see also Py_GetProgramName() */
+    wchar_t *program_name;
 } _PyMainInterpreterConfig;
 
 #define _PyMainInterpreterConfig_INIT \