- Fix a non-observable bug in the typer.
- Add some CHECKs where we rely on not receiving None types.
- Remove an explicit handling of None types where it's redundant and
  misleading (later ToNumeric conversions can again introduce None).

Bug: chromium:965911
Change-Id: I4bb84422de3f9297131e7304216b86884f04ed49
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1630679
Auto-Submit: Georg Neis <neis@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61880}