This is a reland of 93253978

Original change's description:
> Use context of then function for PromiseResolveThenableJob
> 
> When a microtask is executed, we need to use an appropriate,
> non-detached Context for its execution. Currently with
> PromiseResolveThenableJobs [1], the Context used is always drawn from
> the realm of the Promise constructor being used. This may cause
> non-intuitive behavior, such as in the following case:
> 
>   const DeadPromise = iframe.contentWindow.Promise;
>   const p = DeadPromise.resolve({
>     then() {
>       return { success: true };
>     }
>   });
>   p.then(result => { console.log(result); });
> 
>   // Some time later, but synchronously...
>   iframe.src = "http://example.com"; // navigate away.
>   // DeadPromise's Context is detached state now.
>   // p never gets resolved, and its reaction handler never gets called.
> 
> To fix this behavior, when PromiseResolveThenableJob is being queued up,
> the `then` method of the thenable should be used to determine the
> context of the resultant microtask. Doing so aligns with Firefox, and
> also with the latest HTML spec [2][3].
> 
> This change is analogous to CL 1465902, which uses the realm of the
> reaction handlers to determine the Context PromiseReactionJobs run in.
> 
> [1]: https://tc39.es/ecma262/#sec-promiseresolvethenablejob
> [2]: https://html.spec.whatwg.org/C/#enqueuejob(queuename,-job,-arguments)
> [3]: https://github.com/whatwg/html/pull/5212
> 
> Bug: v8:10200
> Change-Id: I2312788eeea0f9e870c13cf3cb5730a87d15609e
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2071624
> Commit-Queue: Timothy Gu <timothygu@chromium.org>
> Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> Reviewed-by: Shu-yu Guo <syg@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#66507}

Bug: v8:10200
Change-Id: I5af003a06c60b0c8cd19de47f847a947d40d046c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2082109Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Timothy Gu <timothygu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66586}