Check for the most commonly used wrong sentinel value (-1). Users
should use cppgc::kSentinelPointer instead.

Bug: chromium:1263009
Change-Id: I200954bcd70c6a100ffec24aece3e1843e1438a0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3242002
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77529}