AttributeDefinition.parser is not consistently used in subclasses

AttributeDefinition includes a 'parser' field but it isn't consistently used for parsing calls in subclasses. ListAttributeDefinition at least isn't using it; it hard codes splitting on ',' forcing attributes that want other delimiters to roll their own parsing (e.g. https://github.com/wildfly/wildfly-core/pull/2408/commits/a3e97f5ebadce19c768af67d1d4d109f3525179d)