{FreePages} is never expected to fail, and each caller wraps the call in
a CHECK macro. In order to learn more about failures, this CL moves the
CHECK inside of {::FreePages}, to fail whenever the {PageAllocator}
fails to free pages.

As a next step, I'll audit our {PageAllocator} implementations to ensure
that none of them return {false} for {FreePages}. Note that this is
already the case for the gin platform (chromium).

R=mlippautz@chromium.org

Bug: v8:12656, chromium:1299735
Change-Id: Ib61be6cc8da0110ead2db1ad005728bd061e0243
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3484321Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79248}