Reorder fields such that often-accessed fields are first. This
minimized generated code size on x86 and x64.

R=titzer@chromium.org

Bug: chromium:839919
Change-Id: Ia2ef9bd2f9a1aa735ed9b1de93cb78aa5d77467b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1538120
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60471}