This is a reland of 8fa7f9ed

Original change's description:
> [runtime] Improve for-in performance
> 
> - Add fast-path String conversion for Smi (which is the most common case)
>   This improves for-in by ~10% on non-initialized enum-caches
> - Don't use the NumberStringCache for large indices to not overflow the cache
>   during key collection. This improves worst-case performance by ~2.5x
> - Drop number_to_string_native and number_to_string_runtime counters
> 
> Bug: v8:7717
> Change-Id: Ic1ff385e3374e6a7e7e7bdb9ae75fb8c238105d1
> Reviewed-on: https://chromium-review.googlesource.com/1167049
> Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Commit-Queue: Camillo Bruni <cbruni@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#55233}

Bug: v8:7717
Change-Id: Ie29041b20ca4a06b8e74a4378e7c1118373072ae
Reviewed-on: https://chromium-review.googlesource.com/1183721
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55316}