This is a reland of ed225df7

Reland changes: removed #if DEBUG from v8.h since it had compile errors
in chromium + windows. Also wasn't needed anyway since the method it was
calling was just a DCHECK.

Original change's description:
> [objects] Cache the ExternalString's data in its resource
>
> For external uncached strings (also called "Small External Strings")
> with cacheable resources, we can cache its resource's data at the
> string's creation time. This allows us to safely read the data from the
> background as we wouldn't trigger a data() callback.
>
> For more information regarding the investigation and possible proposals
> see
> https://docs.google.com/document/d/101eAQqFpBPWFGNJicxtdlwYShJkTOUsEuxkVVeu5Hrk/edit?usp=sharing
>
> Bug: v8:7790, v8:11463
> Change-Id: I6164092b01a6ccb525a9516f476e066b35fb1f96
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2685177
> Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Reviewed-by: Leszek Swirski <leszeks@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#72862}

Bug: v8:7790
Bug: v8:11463
Change-Id: I7c8a54c814b92c8632fb0bcf5a33f57fec159443
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2710440Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72956}