When creating a CatalogColumn, we should use catalogString of a DataType

Right now, the data type field of a CatalogColumn is using the string representation. When we create this string from a DataType object, there are places where we use simpleString. Although catalogString is the same as simpleString right now, it is better to use catalogString. So, we will not introduce issues when we change the semantic of simpleString or the implementation of catalogString.