doc,lib,test: capitalize comment sentences

This activates the eslint capitalize comment rule for comments
above 50 characters.

PR-URL: https://github.com/nodejs/node/pull/24996


Reviewed-By: Ujjwal Sharma <usharma1998@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>