This allows construction and destruction of empty Persistent and
friends, which simplifiest the use for embedders.

Bug: chromium:1056170
Change-Id: I4286639aa5d50f9f98654b859de10bb80cbada21
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2655505
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72396}