async_hooks: add destroy event for gced AsyncResources

In cases where libraries create AsyncResources which may be emitting
more events depending on usage, the only way to ensure that destroy is
called properly is by calling it when the resource gets garbage
collected.

Fixes: https://github.com/nodejs/node/issues/16153
PR-URL: https://github.com/nodejs/node/pull/16998
Fixes: https://github.com/nodejs/node/issues/16153


Reviewed-By: Andreas Madsen <amwebdk@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>