Issue Description:

Assume that you have a private typealias for service results, and you wish to use them in a private extension, then you are presented with an error that the function inside the private extension, needs to be marked as private. It seems that the compiler is not recognising that the code within the extension is already private.

Here is a code example showing the problem:

struct SomeStruct {
  private typealias ServiceResult<T: Decodable> = Result<T, Error>? 
}

private extension SomeStruct {
  // Error reported that 'process' function needs to be private, even though it is within a private extension.
  func process(result: ServiceResult<Int>) { }

  // Works correctly
  private func process2(result: ServiceResult<Int>) { }
}

The same also occurs if you were to declare

private  struct  PrivateStruct { }

Inside of SomeStruct, and then have this as a parameter in a function inside the extension.