This patch added an IsValid method to StartupData which returns a
boolean upon verifying a given snapshot matches the v8 version.
Embedders can use this API now to check snapshots' versions.

This was originally done by Snapshot::CheckVersion, which now simply
runs Startup::IsValid.

Bug: v8:8104
Change-Id: If555bcc55de4a05adf61798cd58d9ea8c8a71302
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2178091
Commit-Queue: Yang Guo <yangguo@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Auto-Submit: Junha Park <jpark3@scu.edu>
Cr-Commit-Position: refs/heads/master@{#67951}