src: do not include partial AsyncWrap instances in heap dump

Heap dumps can be taken either through the inspector or the public API
for it during an async_hooks init() hook, but at that point the
AsyncWrap in question is not done initializing yet and virtual methods
cannot be called on it.

Address this issue (somewhat hackily) by excluding `AsyncWrap`
instances which have not yet executed their `init()` hook fully
from heap dumps.

Fixes: https://github.com/nodejs/node/issues/28786

PR-URL: https://github.com/nodejs/node/pull/28789


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Rich Trott <rtrott@gmail.com>