Adds publicly callable version of write barrier for TracedReferenceBase.

Bug: chromium:1056170
Change-Id: Ie45b4ebbe91d9f0e8f76b521dcbfd931232adcf6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2565248Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71524}