async stack traces

[nitsky]

This PR adds support for async stack traces in a style similar to V8. It supports:

• Async functions and generators.
• Promise chains, including .then(), .catch(), and .finally().
• Promise.all(), Promise.any(), and Promise.allSettled(), with synthetic combinator frames and element indices.
• CallSite.isAsync(), isPromiseAll(), and getPromiseIndex().

For example:

async function fail() {
    await 0;
    throw new Error("boom");
}

async function main() {
    await Promise.all([Promise.resolve(), fail()]);
}

main().catch(error => console.log(error.stack));

The stack now includes the awaiting function and the failing promise’s index:

    at fail (example.js:3:11)
    at async Promise.all (index 1)
    at async main (...)

See also #1248 and #1249.