bpo-42260: Initialize time and warnings earlier at startup (GH-23249)

* Call _PyTime_Init() and _PyWarnings_InitState() earlier during the
  Python initialization.
* Inline _PyImportHooks_Init() into _PySys_InitCore().
* The _warnings initialization function no longer call
  _PyWarnings_InitState() to prevent resetting filters_version to 0.
* _PyWarnings_InitState() now returns an int and no longer clear the
  state in case of error (it's done anyway at Python exit).
* Rework init_importlib(), fix refleaks on errors.

Python/sysmodule.c

@@ -2841,6 +2841,11 @@ _PySys_InitCore(PyThreadState *tstate, PyObject *sysdict)
         }
     }
 
+    /* adding sys.path_hooks and sys.path_importer_cache */
+    SET_SYS("meta_path", PyList_New(0));
+    SET_SYS("path_importer_cache", PyDict_New());
+    SET_SYS("path_hooks", PyList_New(0));
+
     if (_PyErr_Occurred(tstate)) {
         goto err_occurred;
     }