For the --async-stack-traces we can also look through initial parts of
the promise chain that were created by regular Promise#then() calls to
walk up to the first async function frame. This addresses the missing
support for aforementioned example

```js
(async function() {
  await Promise.resolve().then(() =>
    console.log(new Error().stack));
})();
```

which now also works.

Bug: v8:7522
Change-Id: I574943c1fc6ee4a1bd56f208dce78eb7506c5c4f
Reviewed-on: https://chromium-review.googlesource.com/c/1278276Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56613}