The --wasm-fuzzer-gen-test functionality didn't handle imported
functions correctly.

R=manoskouk@chromium.org

Bug: v8:11863
Change-Id: I0486e15465bfabead7bc352d1a94326a39439e43
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3460412Reviewed-by: Manos Koukoutos <manoskouk@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79091}