This would be useful for ForInPrepare. Syntax is unchanged; Torque
should now do the right thing for builtins that return a two-element
struct. More elements than that is still not supported.

Bug: v8:7793
Change-Id: Ic315699402203aba07e906ff6e029834ec0061c6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2596498Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#72171}