[sandbox] Sandboxify WasmIndirectFunctionTable

The WasmIndirectFunctionTable object used to contain a number of raw
pointers to buffers allocated via malloc: the sig_ids and targets
fields. As these were raw pointers, they could be abused by an attacker
to access memory outside of the sandbox, and thereby break out of it.

This CL now simply turns these two buffers into on-heap ByteArrays.

In the future, we'll also need to prevent an attacker from manipulating
the contents of these arrays (at least of the targets array, which
contains function entrypoints), but we'll need additional sandbox
infrastructure before we can do so.

Bug: v8:10391, chromium:1432210
Change-Id: Ide63b241761d97fc110bc7369032e30bc946f295
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/4418966
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Samuel Groß <saelo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#87084}