On operating systems where reserving virtual address space is expensive,
notably Windows pre 8.1, it is not possible to create a proper virtual
memory cage. In order to still be able to reference caged objects
through offsets from the cage base on these systems, this CL introduces
a fake cage mechanism. When the fake cage is used, most of the virtual
memory for the cage is not actually reserved. Instead, the cage's page
allocator simply relies on hints to the OS to obtain pages inside the
cage. This does, however, not provide the same security benefits as a
real cage as unrelated allocations might end up inside the cage.

Bug: chromium:1218005
Change-Id: Ie5314be23966ed0042a017917b63595481b5e7e3
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/+/3217200
Commit-Queue: Samuel Groß <saelo@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77367}