src: use std::vector for setting up process.execPath

Use `std::vector` as an RAII-style alternative to allocating
and deleting raw memory storage.

PR-URL: https://github.com/nodejs/node/pull/25069


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>