gh-105499: Merge typing.Union and types.UnionType (#105511)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
Co-authored-by: Ken Jin <kenjin@python.org>
Co-authored-by: Carl Meyer <carl@oddbird.net>

Include/internal/pycore_unionobject.h

@@ -18,6 +18,7 @@ PyAPI_FUNC(PyObject *) _Py_union_type_or(PyObject *, PyObject *);
 extern PyObject *_Py_subs_parameters(PyObject *, PyObject *, PyObject *, PyObject *);
 extern PyObject *_Py_make_parameters(PyObject *);
 extern PyObject *_Py_union_args(PyObject *self);
+extern PyObject *_Py_union_from_tuple(PyObject *args);
 
 #ifdef __cplusplus
 }