Given that the index we use is checked to be in array index range there is no
need for a costly ToString conversion. All involved helpers for lookup up
properties directly support Smi/HeapNumber indices directly.

Cleanup: Rename GotoUnlessNumberLessThan => GotoIfNumberGreaterThanOrEqual

Change-Id: Iaddc4940f5d984572aa218d568ca71bf694cee74
Reviewed-on: https://chromium-review.googlesource.com/640388
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48039}