Sorting the pages by least free bytes should reduce fragmentation:
since map space is never compacted, it makes sense to first fill
pages that are the most full already rather than to start with the
most empty pages (which is what was more or less going on until this
CL).

Bug: v8:9329
Change-Id: I2157e3b4706c53da80220da5e4a26c00ee4c592f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1735325Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Darius Mercadier <dmercadier@google.com>
Cr-Commit-Position: refs/heads/master@{#63090}