This is a reland of commit 6ec7be21

The issues that caused the CL to be reverted appear to be unrelated
to this change as they still occurred after the revert.

Original change's description:
> [sandbox] Sandboxify WasmExportedFunctionData::sig
>
> This CL changes the WasmExportedFunctionData class to store a direct
> ExternalPointer to the wasm::FunctionSig instead of referencing it
> through a Foreign. This in turn makes it possible to use a unique
> pointer tag for that external pointer when the sandbox is enabled.
>
> Drive-by: move WasmInternalFunction::call_target external pointer to the
> end of the object, in line with other external pointer fields.
>
> Bug: v8:10391, v8:12949
> Change-Id: Ic3ff622a075c9eaa2f8d8835803437466290c928
> 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/+/3829086
> Commit-Queue: Samuel Groß <saelo@chromium.org>
> Reviewed-by: Igor Sheludko <ishell@chromium.org>
> Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#82523}

Bug: v8:10391, v8:12949
Change-Id: I108810ce86b95289dfb6d6377535813deac79a9f
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/+/3838109Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Samuel Groß <saelo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82565}