This is merged into the proposal, move it out of post-mvp flags, and
remove any ifdefs guarding it.

Bug: v8:10993
Change-Id: I4c82e3fc17c97735d5417fa4a5d85d7f091fbb8b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2453457Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70552}