default Collection<? extends AttributeValue> getFlattenedValues() {
        return Collections.singleton(this);
    }
Gets all of the attribute values contained in the attribute value.

<p>This will yield a single result for normal attributes, or a list
of multiple values for projections.

@return Returns the flattened attribute values contained in the attribute value.
smithy-model/src/main/java/software/amazon/smithy/model/selector/AttributeValue.java