bpo-34170: Add _PyCoreConfig.isolated (GH-8417)

* _PyCoreConfig: add isolated and site_import attributes
* Replace Py_IgnoreEnvironment with config->ignore_environment when
  reading the current configuration
* _PyCoreConfig_Read() now sets ignore_environment, utf8_mode,
  isolated and site_import from Py_IgnoreEnvironment, Py_UTF8Mode,
  Py_IsolatedFlag and Py_NoSiteFlag
* _Py_InitializeCore() now sets Py_xxx flags from the configuration
* pymain_read_conf() now uses _PyCoreConfig_Copy() to save/restore
  the configuration.
* Rename _disable_importlib of _PyCoreConfig to _install_importlib
* _PyCoreConfig_SetGlobalConfig() now also set
  Py_HashRandomizationFlag
* Replace !Py_NoSiteFlag with core_config->site_import
diff --git a/Include/internal/pystate.h b/Include/internal/pystate.h
index 6cee272..e041d37 100644
--- a/Include/internal/pystate.h
+++ b/Include/internal/pystate.h
@@ -52,17 +52,17 @@
     wchar_t *program_name;
     /* Set by Py_SetPythonHome() or PYTHONHOME environment variable */
     wchar_t *home;
-    /* isolated and no_site_import are used to set Py_IsolatedFlag and
+    /* isolated and site_import are used to set Py_IsolatedFlag and
        Py_NoSiteFlag flags on Windows in read_pth_file(). These fields
        are ignored when their value are equal to -1 (unset). */
     int isolated;
-    int no_site_import;
+    int site_import;
 } _PyPathConfig;
 
 #define _PyPathConfig_INIT \
     {.module_search_path = NULL, \
      .isolated = -1, \
-     .no_site_import = -1}
+     .site_import = -1}
 /* Note: _PyPathConfig_INIT sets other fields to 0/NULL */
 
 PyAPI_DATA(_PyPathConfig) _Py_path_config;