Since we do not yet have canonicalization for types, when emitting
ref.func in the fuzzer, it is not enough to pick a function whose
signature is equivalent with the requested type; we have to pick a
function that is declared exactly with the requested signature index.

Bug: chromium:1296936
Change-Id: Ie307a9a370bb9ba2c8c334ddf05268ed9c7077d6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3460411Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79081}