Handle recursive type graphs in config binding generator

e.g. Handle recursive type graphs e.g. `MyClass { List<MyClass> }`.
Generator was added in https://github.com/dotnet/runtime/pull/82179. Relevant logic is in the parser. Fix is to cache a new type spec immediately after encountering the `ITypeSymbol`, then initializing the new spec in a late-bound manner (e.g. via a method on the spec type).