doc: clarify ServerResponse explanations

In short: `ServerResponse` acutally inherits from `OutgoingMessage`,
with a series of methods like those in `Stream.Writable`. So we cannot
use `implements`(this has made poeple feel puzzled because there are
still many methods we don't need or have), so `inherits from Stream` is
enough, due to some core reasons and performance told by mcollina from
the ref (See some latest discussions at Ref).

Ref: https://github.com/nodejs/node/issues/14146.
PR-URL: https://github.com/nodejs/node/pull/22305


Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>