worker: support relative paths

This commit adds support for relative paths in Worker.
Paths are relative to the current working directory.

PR-URL: https://github.com/nodejs/node/pull/21407


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Guy Bedford <guybedford@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>