worker: unroll file extension regexp

Refs: https://github.com/nodejs/node/pull/31662#discussion_r377016190

PR-URL: https://github.com/nodejs/node/pull/31779


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Denys Otrishko <shishugi@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>