Update mapping methods in abstract.c to accept frozendict as well as dict

Specifically `PyMapping_GetOptionalItem`, `PyMapping_Keys`, `PyMapping_Values` and `PyMapping_Items`.

Author: da-woods

Objects/abstract.c

@@ -208,7 +208,7 @@ PyObject_GetItem(PyObject *o, PyObject *key)
 int
 PyMapping_GetOptionalItem(PyObject *obj, PyObject *key, PyObject **result)
 {
-    if (PyDict_CheckExact(obj)) {
+    if (PyAnyDict_CheckExact(obj)) {
         return PyDict_GetItemRef(obj, key, result);
     }
 
@@ -2462,7 +2462,7 @@ PyMapping_Keys(PyObject *o)
     if (o == NULL) {
         return null_error();
     }
-    if (PyDict_CheckExact(o)) {
+    if (PyAnyDict_CheckExact(o)) {
         return PyDict_Keys(o);
     }
     return method_output_as_list(o, &_Py_ID(keys));
@@ -2474,7 +2474,7 @@ PyMapping_Items(PyObject *o)
     if (o == NULL) {
         return null_error();
     }
-    if (PyDict_CheckExact(o)) {
+    if (PyAnyDict_CheckExact(o)) {
         return PyDict_Items(o);
     }
     return method_output_as_list(o, &_Py_ID(items));
@@ -2486,7 +2486,7 @@ PyMapping_Values(PyObject *o)
     if (o == NULL) {
         return null_error();
     }
-    if (PyDict_CheckExact(o)) {
+    if (PyAnyDict_CheckExact(o)) {
         return PyDict_Values(o);
     }
     return method_output_as_list(o, &_Py_ID(values));