Moves RO_SPACE to the front of the AllocationSpace enum, so the space
pre-allocation iterations don't miss it. Being at the start of the enum
means that it continues to not be iterated over by any sweeper code,
which iterates from FIRST_GROWABLE_PAGED_SPACE to
LAST_GROWABLE_PAGED_SPACE (renamed from FIRST_PAGED_SPACE and
LAST_PAGED_SPACE).

Bug: v8:7464
Change-Id: I480ba784afbd878552d1cb7f9f5fa57c3b55e004
Reviewed-on: https://chromium-review.googlesource.com/973604
Commit-Queue: Dan Elphick <delphick@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52177}