src: tighten handle scopes for stream operations

Put `HandleScope`s and `Context::Scope`s where they are used,
and don’t create one for native stream callbacks automatically.

This is slightly less convenient but means that stream listeners
that don’t actually call back into JS don’t have to pay the
(small) cost of setting these up.

PR-URL: https://github.com/nodejs/node/pull/18936


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>