As of May 2020 the Google C++ Style Guide suggests using references
for out paramters. Adjust V8's presubmit checks to allow mutable
reference parameters.

Bug: v8:10624
Change-Id: Idcd027892916a14f91ca3bfcb5eba48757cab523
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2252185Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68449}