Investigate Enum Discriminator Type Access Changes

[jorgerangel-msft]

As part of commit there were some unexpected changes made to discriminated enum types that were previously internal and are now generated as public. We should investigate what exact change from this commit caused this. As a test, the ttp/type/model/inheritance/enum-discriminator spector library should have the DogKind and SnakeKind models generated as internal types.