This cl adds support for top level await to d8, but still
does not allow top level await through parsing.
Unfortunately, due to that restriction this cl has no automated
tests, but I added a 'top-level-await' variant and manually
confirmed it passes locally.

Bug: v8:9344
Change-Id: I3528442768107f5ad1ed1e9e947cfceae91c0cc6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1808483
Commit-Queue: Joshua Litt <joshualitt@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63909}