http2: use actual Timeout instances

This makes `Http2Stream`s and `Http2Session`s use actual Timeout
objects in a [kTimeout] symbol property, rather than making the
stream/session itself a timer and appending properties to it directly.

PR-URL: https://github.com/nodejs/node/pull/17704


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>