workers: add test for messagePort.onmessage

PR-URL: https://github.com/nodejs/node/pull/21510


Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Yuta Hiroto <hello@hiroppy.me>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Weijia Wang <starkwang@126.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>