src: update postmortem constant name

This commit renames V8DBG_CLASS_MAP__INSTANCE_ATTRIBUTES__INT
to V8DBG_CLASS_MAP__INSTANCE_TYPE__UINT16_T following upstream changes.

PR-URL: https://github.com/nodejs/node/pull/17489


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Ali Ijaz Sheikh <ofrobots@google.com>