- Add an expected type argument in DecodeWasmInitExprForTesting. This
  eliminates the need to check for kWasmVoid in consume_init_expr.
- Invoke StartDecoding() to initialize module in
  DecodeWasmInitExprForTesting.
- Pass the current module to DecodeInitExprForTesting.
- Adjust tests.

Bug: v8:11895
Change-Id: I13b71b68a2011bf08742701cb9dd986afd6e55f8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2972907
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75292}