after c968607e aka r65078.
CheckedTaggedToArrayIndex is the function that's in sync with the
ICs. It does both more (string-to-index conversion) and less (limit
to kMaxSafeInteger) than CheckedTaggedToInt64.

Bug: chromium:1028021
Change-Id: I992b11b8d4c58b4d3f5385b21998f53dd4b235d2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1934338Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65170}