repl: show proxies as Proxy objects

Before this commit they transparently invoked their magic methods but
that sometimes throws confusing exceptions with misbehaving proxies.

This change is not wholly uncontroversial but we can always change the
default if necessary.  Let's see how it goes.

Fixes: https://github.com/nodejs/node/issues/16483
PR-URL: https://github.com/nodejs/node/pull/16485


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>