bpo-35444: Unify and optimize the helper for getting a builtin object. (GH-11047)

This speeds up pickling of some iterators.

This fixes also error handling in pickling methods when fail to
look up builtin "getattr".
diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index 72cb4c5..a871636 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -3810,6 +3810,7 @@
 static PyObject *
 dictiter_reduce(dictiterobject *di, PyObject *Py_UNUSED(ignored))
 {
+    _Py_IDENTIFIER(iter);
     /* copy the iterator state */
     dictiterobject tmp = *di;
     Py_XINCREF(tmp.di_dict);
@@ -3819,7 +3820,7 @@
     if (list == NULL) {
         return NULL;
     }
-    return Py_BuildValue("N(N)", _PyObject_GetBuiltin("iter"), list);
+    return Py_BuildValue("N(N)", _PyEval_GetBuiltinId(&PyId_iter), list);
 }
 
 PyTypeObject PyDictRevIterItem_Type = {