noextern is the abstract null type for the extern type.

Bug: v8:7748
Change-Id: I03ac0daf3051f479e096f3d05f4fa7cbf03968f1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3810191Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Matthias Liedtke <mliedtke@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82276}