Convert to incremental generators

[Rover656]

I intend to swap from ISourceGenerator to IIncrementalGenerator sometime in the near future.

[PaperPrototype]

I'm really loving the cleaned up api, keep it up! I wonder if I could use this repo while watching this series https://www.youtube.com/watch?v=mwCYZxRrMqo&list=PLCnmpqh8sKKyIWoBCuVHBzmcYBFOj8IyA