deps: backport 4acdb5eec2c from upstream v8

Original commit message:

    Give v8::Eternal a direct reference to the handle.

    This makes it more similar to other handle types (like PersistentBase),
    by simply storing an i::Object** cast to T*. This means that it is not
    necessary to look up the handle in the eternal handles table to access
    the underlying value.

    Like the built-in roots (null, etc.), an eternal handle can never be
    destroyed, so we don't even need to allocate a separate local handle.
    Instead, the Local<T> can point directly at the eternal reference.
    This makes Eternal<T>::Get trivial.

    Review-Url: https://codereview.chromium.org/2751263003
    Cr-Commit-Position: refs/heads/master@{#43912}

Ref: https://github.com/v8/v8/commit/4acdb5eec2c

PR-URL: https://github.com/nodejs/node/pull/12875


Reviewed-By: James M Snell <jasnell@gmail.com>