util: improve format performance

This simplifies the `format()` code and significantly improves the
performance.

PR-URL: https://github.com/nodejs/node/pull/24981


Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>