deps: backport 3700a01c82 from upstream v8

Original commit message:

    Make v8::Eternal::Get and IsEmpty const.

    They do not modify the state of the handle.

    Review-Url: https://codereview.chromium.org/2753973002
    Cr-Commit-Position: refs/heads/master@{#43907}

Ref: https://github.com/v8/v8/commit/3700a01c82

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


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