This fixes the logic in the desugaring of destructuring assignments. In
particular, a spread element would not check if previous `next` results
had already been done, and would always call `next()` again.

Change-Id: I1bd384678722e6cf51c5777fc3b0dd965360291a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2430488
Commit-Queue: Gus Caplan <snek@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70144}