Returns a new URL made by appending a path extension to the original URL.
- iOS 4.0+
- macOS 10.6+
- tvOS 4.0+
- watchOS 2.0+
The path extension to add to the URL.
A new URL with
If the original URL ends with one or more forward slashes, these are removed from the returned URL. A period is inserted between the two parts of the new URL.