Report async tasks to V8 Inspector

Implement a special async-hook listener that forwards information about async tasks to V8Inspector asyncTask* API.

Fixes: https://github.com/nodejs/node/issues/11370

Note: this is an initial (incomplete) version to gather feedback early.

Here are few important items that I would like to discuss besides whatever other feedback you can provide:

• Test coverage. Ideally, we should cover most/all major scenarios, not only setTimeout and Promises. OTOH, I'd rather avoid duplicating all async_hook/async_wrap tests, because that would add too much maintenance burden IMO. Initially, I added only two simple tests - one for promises, the second one for setTimeout. What other scenarios should I add?

• Test assertions. Right now, the tests are only checking whether async stack information is present, the correctness of this information is not verified. Do we want the tests to verify it?

• How to enable/disable inspector async hook when the inspector is started/stopped? I think it's important to enable this hook only when debugging in order to avoid the performance costs of async hooks. However, I was not able to find the right place where to add enable/disable call. Can anybody point me to the right direction please?

There are two test failures right now, I believe they are caused by the fact that inspector async hook is always enabled, while the tests are relying on the async hook machinery to be disabled by default.

People that may be interested in reviewing these changes, based on the git history (the list is almost certainly incomplete): @trevnorris @addaleax @AndreasMadsen @matthewloring @eugeneo

Checklist

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

Affected core subsystem(s)

async_hooks, async_wrap, inspector