Open Radar

 
Downcasting `CIFilters` (or at least the `CIPerspectiveCorrection `, but I suspect the problem is broader) created using convenience methods defined in `CoreImage.CIFilterBuiltins` fails.

My app supports systems older than iOS 13, and I was hoping to support both pre-iOS 13 and the iOS 13 convenience API like so:

```
private let perspectiveFilter: CIFilter = {
        if #available(iOS 13, *) {
            return CIFilter.perspectiveCorrection()
        } else {
            return CIFilter(name: "CIPerspectiveCorrection")!
        }
    }()
```

which then would get used at callsite like such:

```
  if #available(iOS 13, *) {
            guard let filter = perspectiveFilter as? CIPerspectiveCorrection else {
                return nil
            }
```

To my surprise, this guard/let statement fails and returns nil.

I also confirmed this in a simple playground like so:

```
import UIKit
import CoreImage
import CoreImage.CIFilterBuiltins

let filter: CIFilter = CIFilter.perspectiveCorrection()

if let perspectiveFilter = filter as? CIPerspectiveCorrection {
    print("downcast successfull")
} else {
    print("failed")
}
```

which prints out “failed”. 

Tested on iPhone 11 Pro Max / iOS 13.3.1, and iOS 13.3 Simulator bundled with Xcode 11.3.1  (11C505).