This is a reland of 22d894c8
Original change's description:
> [turbofan] Add simplified operator for String.prototype.codePointAt
> 
> This CL adds the simplified operators
>   StringCodePointAt
>   SeqStringCodePointAt
> and associated lowering.
> 
> Bug: v8:7270
> Change-Id: I5aeefddeec39c3119b2d225e92a3116f802e7b45
> Reviewed-on: https://chromium-review.googlesource.com/861789
> Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
> Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
> Reviewed-by: Peter Marshall <petermarshall@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#50547}

Bug: v8:7270
Change-Id: Ia08d18543fc165fc2312cd393ed51f4ec98d7a58
Reviewed-on: https://chromium-review.googlesource.com/866311Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50599}