private String expand(AttributeValue value) {
            StringBuilder builder = new StringBuilder();
            for (Function<AttributeValue, CharSequence> part : parts) {
                builder.append(part.apply(value));
            }
            return builder.toString();
        }
Expands the MessageTemplate using the provided AttributeValue.

<p>Each selector result shape along with the variables that were captured
when the shape was matched are used to create an AttributeValue which
is then passed to this message to create a validation event message.

@param value The attribute value to pass to each part.
@return Returns the expanded message template.
smithy-model/src/main/java/software/amazon/smithy/model/validation/linters/EmitEachSelectorValidator.java