String build() {
            flushRange();
            return token.toString();
        }
Removes leading and trailing quotation mark from the given string. This method will properly unescape whatever
content is withing the string literal as well.

@param str The string to unquote.
@return The unquoted string.
vespajlib/src/main/java/com/yahoo/javacc/UnicodeUtilities.java