bootstrap: move event loop handle checking into snapshot builder

This is only necessary for the snapshot builder (because we
have no way to resurrect the handles at the moment). In addition,
print the handles if the debug flag is set or if the queues
are not empty after snapshot is created.

PR-URL: https://github.com/nodejs/node/pull/39007
Refs: https://github.com/nodejs/node/issues/35711
Refs: https://github.com/nodejs/node/pull/38905


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>