Non-constant SMIs were being shifted to the right with SHR instead of SAR,
which caused corruption of negative offsets.

Add tests for SMI access to arguments using CodeStubArguments.

Change-Id: I6cc4fc0a5dd0018524f5ff4f16f9e9a21866363f
Reviewed-on: https://chromium-review.googlesource.com/854055Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50506}