Those are not safe in combination with the sandbox as they are stored as
raw pointers. Instead of turning them into ExternalPointers (which use
the ExternalPointerTable indirection), this CL simply turns them into
on-heap ByteArrays which is cheaper and should be unproblematic
security-wise as their contents can be corrupted without causing memory
corruption outside the sandbox address space (just incorrect behaviour
and/or further memory corruption *inside* the sandbox, which is fine).

Bug: chromium:1335046
Change-Id: Id2b901a58b7d6c91dd7596fca553d7c76cbc61ec
Cq-Include-Trybots: luci.v8.try:v8_linux64_heap_sandbox_dbg_ng,v8_linux_arm64_sim_heap_sandbox_dbg_ng
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3845636Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Samuel Groß <saelo@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82765}