[3.13] gh-141004: Document PyClassMethod* and PyStaticMethod* APIs (GH-141296) (GH-141309)

gh-141004: Document `PyClassMethod*` and `PyStaticMethod*` APIs (GH-141296)
(cherry picked from commit 807db68)

Co-authored-by: Peter Bierma <zintensitydev@gmail.com>

Author: miss-islington

Doc/c-api/descriptor.rst

@@ -38,3 +38,39 @@ found in the dictionary of type objects.
 
 
 .. c:function:: PyObject* PyWrapper_New(PyObject *, PyObject *)
+
+
+Built-in descriptors
+^^^^^^^^^^^^^^^^^^^^
+
+.. c:var:: PyTypeObject PyClassMethod_Type
+
+   The type of class method objects. This is the same object as
+   :class:`classmethod` in the Python layer.
+
+
+.. c:function:: PyObject *PyClassMethod_New(PyObject *callable)
+
+   Create a new :class:`classmethod` object wrapping *callable*.
+   *callable* must be a callable object and must not be ``NULL``.
+
+   On success, this function returns a :term:`strong reference` to a new class
+   method descriptor. On failure, this function returns ``NULL`` with an
+   exception set.
+
+
+.. c:var:: PyTypeObject PyStaticMethod_Type
+
+   The type of static method objects. This is the same object as
+   :class:`staticmethod` in the Python layer.
+
+
+.. c:function:: PyObject *PyStaticMethod_New(PyObject *callable)
+
+   Create a new :class:`staticmethod` object wrapping *callable*.
+   *callable* must be a callable object and must not be ``NULL``.
+
+   On success, this function returns a :term:`strong reference` to a new static
+   method descriptor. On failure, this function returns ``NULL`` with an
+   exception set.
+