v8: add cachedDataVersionTag

Adds `v8.cachedDataVersionTag()`, which returns an integer
representing the version tag for `cachedData` for the current V8
version & flags.

PR-URL: https://github.com/nodejs/node/pull/11515


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>