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

(cherry picked from commit 0319cd68)

Co-authored-by: Dong-hee Na <donghee.na@python.org>

Doc/library/functions.rst

@@ -1509,6 +1509,8 @@ 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)