Implement TCGC's Model Types

[iscai-msft]

Language emitters should work to move entirely to TCGC's new ecosystem. I've created a separate issue if people want to first move to the SdkModelType and SdkEnumType. To access these types, you can access and on the type

[iscai-msft]

Python has supported only getting models and enum types from TCGC types for a long time. This work was finished mid-2023