This Objective-C method
```
- (void)stream:(NSStream *)aStream
handleEvent:(NSStreamEvent)eventCode;
```
should be imported as
```
optional func stream(
_ aStream: Stream,
handle eventCode: Stream.Event)
```
and not
```
optional func stream(
_ aStream: Stream,
handleEvent eventCode: Stream.Event)
```
in order to stay compatible with Objective-C interop mode.
rdar://113208675
