os: use uv_os_gethostname() in hostname()

This commit changes the C++ implementation of os.hostname()
to use uv_os_gethostname().

PR-URL: https://github.com/nodejs/node/pull/25111


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>