`StringUtil::CharacterCount` should return the length of underlying
representation storage of a protocol string.
`StringUtil::CharacterCount` is only used in DictionaryValue
serialization. Only `Network.Headers` is an object type, represented
with DictionaryValue.
PR-URL: https://github.com/nodejs/node/pull/56788
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Daniel Lemire <daniel@lemire.me>
Reviewed-By: Kohei Ueno <kohei.ueno119@gmail.com>
