The localeCompare for ASCII chars needs to expand the string contents
from one-byte representation into two-byte representation, which
requires memory copy. This CL skips the representation conversion by
using compareUTF8. It can improve the JetStream2 cdjs case by 21% on
my machine.

Change-Id: I3841dc700e36744aadd9a1ff9fa7d93c84dc04fd
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1624705
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62408}