process: add `'worker'` event

Provides a new `process.on('worker', (worker) => {})` event that
is triggered by the creation of a new `worker_thread.Worker`.
The use case is to allow hooks to be installed for monitoring
workers without having to modify the call sites around those.

Signed-off-by: James M Snell <jasnell@gmail.com>

PR-URL: https://github.com/nodejs/node/pull/38659


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>