src: add DCHECK macros

This adds check statements for debugging and refactors the code
accordingly.

PR-URL: https://github.com/nodejs/node/pull/24359


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>