net: use actual Timeout instance on Sockets

This makes `net.Sockets` use actual Timeout objects in a `[kTimeout]`
symbol property, rather than making the socket itself a timer and
appending properties to it directly.

This should make the code generally easier to understand, and might
also prevent some deopts from properties being changes on the socket
itself.

Also moves the Timeout constructor into an internal module.

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>