[v12.x] src: render N-API weak callbacks as cleanup hooks

[gabrielschulhof]

Since worker threads are complete Node.js environments, including the
ability to load native addons, and since those native addons can
allocate resources to be freed when objects go out of scope, and since,
upon worker thread exit, the engine does not invoke the weak callbacks
responsible for freeing resources which still have references, this
modification introduces tracking for weak references such that a list
of outstanding weak references is maintained. This list is traversed
during environment teardown. The callbacks for the remaining weak
references are called.

This change is also relevant for Node.js embedder scenarios, because in
those cases the process also outlives the node::Environment and
therefore weak callbacks should also be rendered as environment cleanup
hooks to ensure proper cleanup after native addons. This changes
introduces the means by which this can be accomplished.

A benchmark is included which measures the time it takes to execute the
weak reference callback for a given number of weak references.

Re: tc39/proposal-weakrefs#125 (comment)
PR-URL: #28428
Reviewed-By: @addaleax
Reviewed-By: @mhdawson

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• commit message follows commit guidelines

[addaleax]

(As a note for reviewers, the contents are identical to those of the original PR)

[gabrielschulhof]

Yeah, it was a clean cherry-pick.

[gabrielschulhof]

I moved the addition of benchmark/napi/ref/.gitignore from the backport of #29995 (#30072) to this backport, because with it, #30072 will not pass make bench-addons-build && tools/test.py test/benchmark/test-benchmark-napi.js.

This way, at least one of the two PRs will pass that test, and, once they both land, the result should also pass.

[targos]

Thanks for opening the PR, but if this is a clean cherry-pick, I'm a bit confused about why we don't land this change (along with #30072) in v12.x using the regular release process?

[gabrielschulhof]

@targos I wanted to make sure it gets into v12.x because of the comments at nodejs/node-addon-api#567 (comment) and below.

[mhdawson]

@gabrielf I think @targos just meant that they should be backported following this guidance: https://github.com/nodejs/node/blob/master/doc/guides/backporting-to-release-lines.md

[targos]

The original commit landed on v12.x-staging.