inspector: allow concurrent inspector sessions

This change enables concurrent inspector sessions, through WebSocket
interface as well as JS interface, in any combination.

PR-URL: https://github.com/nodejs/node/pull/20137


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>