As sandboxed pointers are now default-enabled when the sandbox is
enabled, it is no longer possible to deactivate the sandbox at runtime.
This CL therefore removes all the logic that was required to support a
sandbox that could be disabled at runtime, moves the initialization of
the sandbox into V8::Initialize, and deprecates V8::InitializeSandbox.

This change also makes the sandbox initialization deterministic if
FLAG_random_seed is supplied.

Bug: v8:10391
Change-Id: Ibd49f7c251b7c58c642f18a551ecc2c391740970
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/+/3762583Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Samuel Groß <saelo@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81746}