Specialization of member descriptors only handles `Py_T_OBJECT_EX` but `_Py_T_OBJECT` seems more common

[markshannon]

Despite _Py_T_OBJECT being marked as deprecated in descrobject.h it is commonly used in the standard library.
LOAD_ATTR_SLOT de-optimizes if the stored value is NULL. If the stored value is not NULL, both _Py_T_OBJECT and Py_T_OBJECT_EX act the same, so we can reuse LOAD_ATTR_SLOT for _Py_T_OBJECT.

For storing attributes, _Py_T_OBJECT and Py_T_OBJECT_EX are exactly the same.

I don't know why _Py_T_OBJECT is deprecated, the semantics seem quite reasonable.

Linked PRs

• GH-111772: Specialize slot loads and stores for _Py_T_OBJECT #111773