This change fixes the premature exit of worker threads when there are still
remaining pending ops.
This change reuses the idea of #22647 (unref'ing `op_worker_recv_message` in
worker threads if closeOnIdle specified) and uses
`web_worker.has_message_event_listener` check in the opposite way as
#22944. (Now we continue the worker when `has_message_event_listener` is
true instead of stopping it when `has_message_event_listener` is false.
closes #23061
closes #26154
cc8e339c25