node-api: define version 8

Mark as stable the APIs that define Node-API version 8.

PR-URL: https://github.com/nodejs/node/pull/37652


Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>
Reviewed-By: Michael Dawson <midawson@redhat.com>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>