Changes:
- Unpack packed typed in arrays/structs where needed.
- i8 should have log-size 0.
- Use typed-funcref feature flag instead of gc where appropriate.
- Set argument indexes correctly for gc opcodes in
  function-body-decoder.
- Remove no-longer valid TODOs.

Bug: v8:7748
Change-Id: I1a73794d0f93da6c7177e496d47df4106031f0eb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2230520
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68196}