addDelegate method
Adds a delegate to this NSWindowDelegateHandler.
Returns a NSWindowDelegateHandle which can be used to remove the delegate from this handler.
Example:
final someDelegate = ...
final handler = NSWindowDelegateHandler();
final handle = handler.addDelegate(someDelegate);
...
handle.removeFromHandler();
Implementation
NSWindowDelegateHandle addDelegate(NSWindowDelegate delegate) {
final handle = NSWindowDelegateHandle.create(this);
delegates[handle] = delegate;
return handle;
}