V2 Generic Improvements

* [ ] generic dataclasses
* [x] a `TypedDict` to gather [these](https://github.com/pydantic/pydantic/blob/06b8bdc6f07f12a15f5f0ba79e38f4a509803328/pydantic/main.py#L183-L188)
* [x] as @dmontagu mentioned, generic tests looks slow - is this indicative of generics being slow? Can we sort it by caching core-schema if there are no generic arguments?