Issue #14383: Add _PyDict_GetItemId() and _PyDict_SetItemId() functions

These functions simplify the usage of static constant Unicode strings.
Generalize the usage of _Py_Identifier in ceval.c and typeobject.c.
diff --git a/Include/dictobject.h b/Include/dictobject.h
index ed44e20..63c810e 100644
--- a/Include/dictobject.h
+++ b/Include/dictobject.h
@@ -155,7 +155,9 @@
                                            int override);
 
 PyAPI_FUNC(PyObject *) PyDict_GetItemString(PyObject *dp, const char *key);
+PyAPI_FUNC(PyObject *) _PyDict_GetItemId(PyObject *dp, struct _Py_Identifier *key);
 PyAPI_FUNC(int) PyDict_SetItemString(PyObject *dp, const char *key, PyObject *item);
+PyAPI_FUNC(int) _PyDict_SetItemId(PyObject *dp, struct _Py_Identifier *key, PyObject *item);
 PyAPI_FUNC(int) PyDict_DelItemString(PyObject *dp, const char *key);
 
 #ifdef __cplusplus