This change updates verifier generation to:
- Fix a bug I introduced in https://crrev.com/c/2047399 that caused
  values within struct-typed fields to not get verified
- Support indexed fields with start offsets that are not known at
  compile time
- Support indexed fields with complex length expressions

Bug: v8:7793
Change-Id: I5ae8803fce59abae0989fcb094bd9692cd88e38e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2461456
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70490}