This adds a new operator LookupSigned32HashStorageIndex, which is a
specialization of the general LookupHashStorageIndex for Map#get that
is used when TurboFan knows that the key is in Signed32 range.

This improves the execution time of the ARES6 Basic test locally by
around 5% and seems to make sense in general.

Bug: v8:6410, v8:6354, v8:6278, v8:6344
Change-Id: I78dcbc9cc855a4109e1690d8cd14fbc88fd89861
Reviewed-on: https://chromium-review.googlesource.com/706787Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48361}