src: rename StreamWrap to LibuvStreamWrap

This should help clarify what kind of resource a `StreamWrap`
represents.

PR-URL: https://github.com/nodejs/node/pull/16157


Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>