This is a reland of 65070355

Original change's description:
> [ia32,root] Add indirect calls and jumps through virtual register
>
> This adds a temporary mechanism for isolate-independent calls and
> jumps.  The problem was that - as ia32 doesn't have a scratch register
> - Call and Jump cannot call through a register. This CL adds a
> so-called virtual register (= a pointer-sized field) on IsolateData.
>
> The virtual register can be removed once pc-relative calls are
> implemented and all builtins have been embedded.
>
> Bug: v8:6666
> Change-Id: I1f9d8a25643fad0b3919dd813dbe219d20fcc6bc
> Reviewed-on: https://chromium-review.googlesource.com/c/1282991
> Commit-Queue: Jakob Gruber <jgruber@chromium.org>
> Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
> Reviewed-by: Igor Sheludko <ishell@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#56693}

TBR=sigurds@chromium.org

Bug: v8:6666
Change-Id: If463e68036673c7873d0d5e1a8a01ef31263cbfa
Reviewed-on: https://chromium-review.googlesource.com/c/1283052
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56700}