Dataset configuration doesn't support complex objects for registered classes
like this. In order for the discover entity to be migration to YAML, there needs
to be a different way to initialize this class that can be encoded in YAML.

This mapper is checking if a column name exists in the ColumnSet. That check
compares against the flattened column name stored in the ColumnSet. This can be
achieved by comparing to a normal set instead of a ColumnSet.