worker,src: display remaining handles if `uv_loop_close` fails

Right now, we crash the process if there are handles remaining
on the event loop when we exit (except for the main thread).

This does not provide a lot of information about causes, though;
in particular, we don’t show which handles are pending and
who own them.

This patch adds debug output to these cases to help with the
situation.

PR-URL: https://github.com/nodejs/node/pull/21238


Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>