Abstract reference types in the fuzzer have only generated trivial
values. This CL adds the capability for them to generate values of their
subtypes in addition.
Drive-by: Fix emission of multiple tables in wasm-fuzzer-common.

Bug: v8:11954
Change-Id: Id434109c9ae6c1e1b799414c90f18180b8895755
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3109672
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76430}