This reverts commit 81c34968 and also
490f3580 which depends on the former.

Reason for revert: Break CFI tests in chromium https://ci.chromium.org/p/chromium/builders/ci/Linux%20CFI/17438
Original change's description:
> [heap] Make ReadOnlySpace use bump pointer allocation
>
> This changes ReadOnlySpace to no longer be a PagedSpace but instead it
> is now a BaseSpace. BasicSpace is a new base class that Space inherits
> from and which has no allocation methods and does not dictate how the
> pages should be held.
>
> ReadOnlySpace unlike Space holds its pages as a
> std::vector<ReadOnlyPage>, where ReadOnlyPage directly subclasses
> BasicMemoryChunk, meaning they do not have prev_ and next_ pointers and
> cannot be held in a heap::List. This is desirable since with pointer
> compression we would like to remap these pages to different memory
> addresses which would be impossible with a heap::List.
>
> Since ReadOnlySpace no longer uses most of the code from the other
> Spaces it makes sense to simplify its memory allocation to use a simple
> bump pointer and always allocate a new page whenever an allocation
> exceeds the remaining space on the final page.
>
> Change-Id: Iee6d9f96cfb174b4026ee671ee4f897909b38418
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2209060
> Commit-Queue: Dan Elphick <delphick@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#68137}

TBR=ulan@chromium.org,delphick@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I68c9834872e55eb833be081f8ff99b786bfa9894
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2232552
Commit-Queue: Dan Elphick <delphick@chromium.org>
Reviewed-by: Dan Elphick <delphick@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68211}