This enables the embedder to check if the snapshot generated
from SnapshotCreator::CreateBlob() can be rehashed and the seed
can be recomputed during deserialization.

The lack of this functionality resulted in a temporary vunerability
in Node.js: https://github.com/nodejs/node/pull/27365

Change-Id: I88d52337217c40f79c26438be3c87d2db874d980
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1578661
Commit-Queue: Joyee Cheung <joyee@igalia.com>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61175}