[red-knot] fix scope inference with deferred types

[carljm]

Test coverage for #13131 wasn't as good as I thought it was, because although we infer a lot of types in stubs in typeshed, we don't check typeshed, and therefore we don't do scope-level inference and pull all types for a scope. So we didn't really have good test coverage for scope-level inference in a stub. And because of this, I got the code for supporting that wrong, meaning that if we did scope-level inference with deferred types, we'd end up never populating the deferred types in the scope's TypeInference, which causes panics like #13160.

Here I both add test coverage by running the corpus tests both as .py and as .pyi (which reveals the panic), and I fix the code to support deferred types in scope inference.

This also revealed a problem with deferred types in generic functions, which effectively span two scopes. That problem will require a bit more thought, and I don't want to block this PR on it, so for now I just don't defer annotations on generic functions.

Fixes #13160.

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