This reverts commit f731e13f.

Reason for revert: perf regressions, chromium:1179757

Original change's description:
> Remove 'length' field from ScopeInfo
>
> ScopeInfo has a vestigial 'length' field from when it used to be a
> FixedArray. This change removes that field, which saves some memory.
>
> More specifically:
>
> - Make ScopeInfo inherit from HeapObject, not FixedArrayBase which
>   supplied the 'length' field.
> - Privatize the FixedArray-style functions that provide access to
>   ScopeInfo fields by index, and move them from scope-info-inl.h to
>   scope-info.cc. Those functions are still used pretty heavily during
>   initialization (ScopeInfo::Create, etc.), but at least we can avoid
>   presenting them to the rest of the world.
> - Change FactoryBase::NewScopeInfo to allocate the updated object shape.
>   It maintains the existing behavior of filling the newly-allocated
>   object with undefined, even though that's not a valid ScopeInfo and
>   further initialization is required.
> - Move part of AccessorAssembler::ScriptContextTableLookup into a new
>   Torque macro, because it used to rely on casting ScopeInfo to
>   FixedArrayBase.
> - In V8HeapExplorer::AddEntry, don't claim that ScopeInfo objects are
>   arrays. I think it makes more sense to list them under "(system)" in
>   the dev tools, like most other V8 internal types.
>
> Bug: v8:8952
> Change-Id: I8278e3a90027d4409f0d268da0fe7080754c6b8c
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2601880
> Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> Reviewed-by: Peter Marshall <petermarshall@chromium.org>
> Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
> Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
> Reviewed-by: Mythri Alle <mythria@chromium.org>
> Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
> Cr-Commit-Position: refs/heads/master@{#72830}

Bug: v8:8952
Change-Id: I00a69da79e5ac6aaae4436a41ce773ae014cc775
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2706086
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Seth Brenith <seth.brenith@microsoft.com>
Commit-Queue: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72855}