Currently, PageAllocator assumes that FreePages(start, size) will always
be called on the same region that was passed to AllocatePages(start,
size). This assumption is made in:
1) leak-sanitizer (LsanPageAllocator) that checks it explicitly,
2) on Windows, FreePages() calls VirtualFree() with zero-size and
   MEM_RELEASE, which causes the entire reservation to be freed.

The CL temporarily fixes the bot failures just by holding the unneeded
half and adds a TODO to return the unneded part back to the OS.

Bug: chromium:1325007
Change-Id: I2bd878876d43d693cf2138020f410ffe1615b4e9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3695363Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81059}