deps: V8: backport b49206d from upstream

This is the v8.x backport of https://github.com/nodejs/node/pull/20727.

Original commit message:
  ThreadDataTable: Change global linked list to per-Isolate hash map.

  For use cases with a large number of threads or a large number of
  isolates (or both), ThreadDataTable can be a major performance
  bottleneck due to O(n) lookup time of the linked list. Switching to a
  hash map reduces this to O(1).

  Example 1: Sandstorm.io, a Node.js app that utilizes "fibers", was
  observed spending the majority of CPU time iterating over the
  ThreadDataTable.
  See: https://sandstorm.io/news/2016-09-30-fiber-bomb-debugging-story

  Example 2: Cloudflare's Workers engine, a high-multi-tenancy web
  server framework built on V8 (but not Node), creates large numbers of
  threads and isolates per-process. It saw a 34x improvement in
  throughput when we applied this patch.

  Cloudflare has been using a patch in production since the Worker
  launch which replaces the linked list with a hash map -- but still
  global.

  This commit builds on that but goes further and creates a separate
  hash map and mutex for each isolate, with the table being a member of
  the Isolate class. This avoids any globals and should reduce lock
  contention.

  Bug: v8:5338
  Change-Id: If0d11509afb2e043b888c376e36d3463db931b47
  Reviewed-on: https://chromium-review.googlesource.com/1014407


Reviewed-by: Yang Guo <yangguo@chromium.org>
  Commit-Queue: Yang Guo <yangguo@chromium.org>
  Cr-Commit-Position: refs/heads/master@{#52753}

Backport-PR-URL: https://github.com/nodejs/node/pull/21529
PR-URL: https://github.com/nodejs/node/pull/20727
Refs: https://github.com/nodejs/node/issues/20083
Refs: https://github.com/nodejs/node/issues/20083


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>