AccessCheckInfo is a struct which is initialized with undefined values
as placeholders. Update the definiton so that the verifier that could
run between allocation and setting a field is happy.

Bug: chromium:967433
Change-Id: I21b99645c01e109d7ba0b61a5366e1f66a7f98d5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1634922Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61918}