pythongh-96197: Define the behavior of repr if sys.displayhook is lost

Author: corona10

Doc/library/functions.rst

@@ -1513,6 +1513,8 @@ 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 available to be called, this function will
+   raise :exc:`RuntimeError`.
 
 
 .. function:: reversed(seq)