Currently, when compiling with V8_VIRTUAL_MEMORY_CAGE enabled, the
behavior of the BoundedPageAllocator changes from simply making freed
pages inaccessible to decommitting them, which guarantees that they will
be zero-initialized after the next allocation. As this seems to cause
some performance regressions on Mac, this CL introduces a new enum that
specifies how the allocator should behave:
kAllocatedPagesMustBeZeroInitialized causes the pages to be decommitted
during FreePages() and ReleasePages() and thus guarantees
zero-initialization during AllocPages().
kAllocatedPagesCanBeUninitialized only causes the pages to be made
inaccessible, and so does not generally guarantee zero-initialization
for AllocPages().

Finally, this CL also removes some dead code in allocation.cc.

Bug: chromium:1257089
Change-Id: I53fa52c8913df869bee2b536efe252780d1ad893
Cq-Include-Trybots: luci.v8.try:v8_linux64_heap_sandbox_dbg_ng
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3208812
Commit-Queue: Samuel Groß <saelo@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77285}