util: expose toUSVString

Expose toUSVString so it can be used by user libraries.

PR-URL: https://github.com/nodejs/node/pull/39814
Refs: https://github.com/nodejs/undici/pull/986


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>