n-api: finalize during second-pass callback

Calling into the engine from a weak callback is unsafe, however, the
engine offers a way to attach a second-pass weak callback which gets
called when it is safe to call into JavaScript. This moves the point
at which the N-API finalize callback gets called to this latter point.

Fixes: https://github.com/nodejs/node/issues/25927
PR-URL: https://github.com/nodejs/node/pull/25992
Backport-PR-URL: https://github.com/nodejs/node/pull/26060


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>