Produce the same scopes / variables for parameters (part 3).

This CL fixes the ordering + variable types in PreParser when there are
simple parameters + a rest parameter. In that case, Parser declares
unnamed temporaries for the non-rest params, then the rest param, then
the named variables (which are not parameters) for the non-rest params.

BUG=v8:5516
R=vogelheim@chromium.org

Change-Id: I9b006595039c8002b0508d1d2a200aa9a0f3eae0
Reviewed-on: https://chromium-review.googlesource.com/443527Reviewed-by: Daniel Vogelheim <vogelheim@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43241}