gh-96197: Define the behavior of repr if sys.displayhook is lost (gh-96242)

Doc/library/functions.rst

@@ -1515,6 +1515,8 @@ are always available.  They are listed here in alphabetical order.
    of the type of the object together with additional information often
    including the name and address of the object.  A class can control what this
    function returns for its instances by defining a :meth:`__repr__` method.
+   If :func:`sys.displayhook` is not accessible, this function will raise
+   :exc:`RuntimeError`.
 
 
 .. function:: reversed(seq)