* add unicode_ci interface * fix build * fix check * fix test * change comments * add test * Update util/collate/unicode_ci.go Co-authored-by: djshow832 <zhangming@pingcap.com> Co-authored-by: djshow832 <zhangming@pingcap.com> Co-authored-by: Yuanjia Zhang <zhangyuanjia@pingcap.com> Co-authored-by: djshow832 <873581766@qq.com> Co-authored-by: ti-srebot <66930949+ti-srebot@users.noreply.github.com>