Add a conversion to int32 index for Numbers and Strings containing
indices, and change the element bounds check / lookup nodes to take an
int32 rather than a Smi. While we're at it, also turn the index node
into an int32 index different depending on its known representation.

Bug: v8:7700, v8:13287
Change-Id: Ie98502d58f789873d42f8801499e78bf777db70f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3900012
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83291}