Minor fix for javadoc (applicable for java 11). (#32573)

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/expression/function/scalar/string/StringFunctionUtils.java

@@ -33,7 +33,7 @@ static String substring(String s, int start, int length) {
     }
 
     /**
-     * Trims the trailing whitespace characters from the given String. Uses java.lang.Character.isWhitespace(char)
+     * Trims the trailing whitespace characters from the given String. Uses {@link Character#isWhitespace(char)}
      * to determine if a character is whitespace or not.
      *
      * @param s       the original String