Modify `_http_outgoing.ts` to support the extended signature of
`validateHeaderName()` used since node v19.5.0/v18.14.0 by adding the
`label` parameter. (see:
https://nodejs.org/api/http.html#httpvalidateheadernamename-label)
Making both validation functions accessible as public exports of
`node:http`
Fixes: #22614
