n-api: define release 6

Mark all N-APIs that have been added since version 5 as stable.

PR-URL: https://github.com/nodejs/node/pull/32058
Fixes: https://github.com/nodejs/abi-stable-node/issues/393


Co-Authored-By: legendecas <legendecas@gmail.com>
Signed-off-by: Gabriel Schulhof <gabriel.schulhof@intel.com>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>