assert,util: harden comparison

The former algorithm used checks which were unsafe. Most of these
have been replaced with alternatives that can not be manipulated or
fooled that easily.

PR-URL: https://github.com/nodejs/node/pull/24831


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ujjwal Sharma <usharma1998@gmail.com>