Add Xcode 26 build support

Since OS 26 SDK, `UIKit` and `AppKit` will export SwiftUICore.

Update the `OpenSwiftUI_SPI` part to avoid `OSUICore` -> `SUICore`

```
OSUICore -> OSUI_SPI (C module) -> AppKit -> SUICore (conflict).
```

Also this will only happen if the target is >= SwiftUI_v1. By default if we do not specify platform on Package, it will use `arm64-apple-macos10.13`.