AlterTypeStatement validate is missing checks

All the checks for a valid AlterTypeStatement are happening in apply() not validate()

Same problem in CreateTypeStatement.  https://github.com/apache/cassandra/blob/45f4f8c1e89e4b221b569ff3bd3e78675eff7747/src/java/org/apache/cassandra/cql3/statements/schema/CreateTypeStatement.java#L66

Perhaps all schema statements should be checked for validations