Rather than using a page allocator and rounding all allocation request
sizes up to the next multiple of the OS page size, we now use a
base::RegionAllocator with a "page size" of 128 as a compromise between
the number of regions it needs to manage and the amount of wasted memory
due to allocations being rounded up to a multiple of that page size.
While this is still not as performant as a "real" allocator, it does
noticeably improve performance when allocating lots of ArrayBuffers.

Bug: chromium:1340224
Change-Id: I56d1ab066ba55710864bdad048fb620078b2d8c2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3913346
Commit-Queue: Samuel Groß <saelo@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83396}