bpo-34170: Add _Py_InitializeFromConfig() (GH-8454)

* If _Py_InitializeCore() is called twice, the second call now copies
  and apply (partially) the new configuration.
* Rename _Py_CommandLineDetails to _PyCmdline
* Move more code into pymain_init(). The core configuration created
  by Py_Main() is new destroyed before running Python to reduce the
  memory footprint.
* _Py_InitializeCore() now returns the created interpreter.
  _Py_InitializeMainInterpreter() now expects an interpreter.
* Remove _Py_InitializeEx_Private(): _freeze_importlib now uses
  _Py_InitializeFromConfig()
* _PyCoreConfig_InitPathConfig() now only computes the path
  configuration if needed.
diff --git a/Include/pystate.h b/Include/pystate.h
index 84428bc..fe14832 100644
--- a/Include/pystate.h
+++ b/Include/pystate.h
@@ -200,8 +200,7 @@
     /* --- Private fields -------- */
 
     /* Install importlib? If set to 0, importlib is not initialized at all.
-       Needed by freeze_importlib: see install_importlib argument of
-       _Py_InitializeEx_Private(). */
+       Needed by freeze_importlib. */
     int _install_importlib;
 
     /* Value of the --check-hash-based-pycs configure option. Valid values: