This is useful for the upcoming "huge TypedArrays" support, to be able
to quickly decide in stubs/generated code whether a string used as the
key for a property load/store can possibly be an exotic integer index.

Bug: v8:4153
Change-Id: I50ce655d2f78fb36e5615fd580f22c9290216c84
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1821460
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64165}