embedding: make Stop() stop Workers

This makes sense given that terminating execution of the parent thread
this way likely also is supposed to stop all running Worker threads
spawned by it.

PR-URL: https://github.com/nodejs/node/pull/32531


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>