deps: cherry-pick a8f6869 from upstream V8

Original commit message:

    [debug] Fully implement Debug::ArchiveDebug and Debug::RestoreDebug.

    I have a project that embeds V8 and uses a single `Isolate` from multiple
    threads. The program runs just fine, but sometimes the inspector doesn't
    stop on the correct line after stepping over a statement that switches
    threads behind the scenes, even though the original thread is restored by
    the time the next statement is executed.

    After some digging, I discovered that the `Debug::ArchiveDebug` and
    `Debug::RestoreDebug` methods, which should be responsible for
    saving/restoring this `ThreadLocal` information when switching threads,
    currently don't do anything.

    This commit implements those methods using MemCopy, in the style of other
    Archive/Restore methods in the V8 codebase.

    Related: https://groups.google.com/forum/#!topic/v8-users/_Qf2rwljRk8

    Note: I believe my employer, Meteor Development Group, has previously
    signed the CLA using the group email address google-contrib@meteor.com.

    R=yangguo@chromium.org,jgruber@chromium.org
    CC=info@bnoordhuis.nl

    Bug: v8:7230
    Change-Id: Id517c873eb81cd53f7216c7efd441b956cf7f943
    Reviewed-on: https://chromium-review.googlesource.com/833260


    Commit-Queue: Yang Guo <yangguo@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#54902}

Refs: https://github.com/v8/v8/commit/a8f6869177685cfb9c199c454a86f4698c260515

PR-URL: https://github.com/nodejs/node/pull/21983


Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Ujjwal Sharma <usharma1998@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>