src: use struct as arguments to node::Assert

This just makes the code a bit more obvious (subjectively).

PR-URL: https://github.com/nodejs/node/pull/25869


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>