Add inbounds benchmark for String.p.charCodeAt
and add in and out of bounds benchmarks for
String.p.codePointAt.

Bug: v8:7092, v8:7326, chromium:806758
Change-Id: I48065627bd79d8fb24e55b2f6dce590e7adbbd6e
Reviewed-on: https://chromium-review.googlesource.com/891858Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50942}