public static Substring ofExpressions(ToExpression expression, int startIndex, int stopIndex, boolean reverse) {
        return ofExpressions(expression, Expression.of(startIndex), Expression.of(stopIndex), Expression.of(reverse));
    }
Creates a {@link Substring} function from the given expressions.

@param expression the string to extract from.
@param startIndex the starting index.
@param stopIndex  the ending index.
@param reverse    the reverse order argument.
@return The resulting {@link Substring} function.
smithy-rules-engine/src/main/java/software/amazon/smithy/rulesengine/language/syntax/expressions/functions/Substring.java