private static char lowSurrogate(int codePoint) {
            return (char) (MIN_LOW_SURROGATE + (codePoint & 0x3ff));
        }
Returns the actual value of the trailing byte (removes the prefix '10') for composition.
jraft-core/src/main/java/com/alipay/sofa/jraft/util/internal/UnsafeUtf8Util.java