- Add private NewStructInternal
- Dehandlify JSObject initializers

Bug: v8:11263
Change-Id: I62d77ef32747c2042de707ba10fad20327af0930
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2729342Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73157}