[CarPlay] Propagate constructors to derived classes. Fixes #15169.

In Objective-C constructors are automatically visible in derived classes as
well, but we need to replicate such constructors explicitly in derived
classes.

Fixes #15169.

src/carplay.cs

@@ -1723,6 +1723,9 @@ interface CPNowPlayingImageButton
 		[Export ("initWithImage:handler:")]
 		NativeHandle Constructor (UIImage image, [NullAllowed] Action<CPNowPlayingButton> handler);
 
+		[Export ("initWithHandler:")]
+		NativeHandle Constructor ([NullAllowed] Action<CPNowPlayingButton> handler);
+
 		[NullAllowed, Export ("image", ArgumentSemantic.Strong)]
 		UIImage Image { get; }
 	}
@@ -1926,23 +1929,38 @@ interface CPContactMessageButton
 
 	[NoWatch, NoTV, NoMac, iOS (14,0)]
 	[BaseType (typeof (CPNowPlayingButton))]
-	interface CPNowPlayingShuffleButton {}
+	interface CPNowPlayingShuffleButton {
+		[Export ("initWithHandler:")]
+		NativeHandle Constructor ([NullAllowed] Action<CPNowPlayingButton> handler);
+	}
 
 	[NoWatch, NoTV, NoMac, iOS (14,0)]
 	[BaseType (typeof (CPNowPlayingButton))]
-	interface CPNowPlayingAddToLibraryButton {}
+	interface CPNowPlayingAddToLibraryButton {
+		[Export ("initWithHandler:")]
+		NativeHandle Constructor ([NullAllowed] Action<CPNowPlayingButton> handler);
+	}
 
 	[NoWatch, NoTV, NoMac, iOS (14,0)]
 	[BaseType (typeof (CPNowPlayingButton))]
-	interface CPNowPlayingMoreButton {}
+	interface CPNowPlayingMoreButton {
+		[Export ("initWithHandler:")]
+		NativeHandle Constructor ([NullAllowed] Action<CPNowPlayingButton> handler);
+	}
 
 	[NoWatch, NoTV, NoMac, iOS (14,0)]
 	[BaseType (typeof (CPNowPlayingButton))]
-	interface CPNowPlayingPlaybackRateButton {}
+	interface CPNowPlayingPlaybackRateButton {
+		[Export ("initWithHandler:")]
+		NativeHandle Constructor ([NullAllowed] Action<CPNowPlayingButton> handler);
+	}
 
 	[NoWatch, NoTV, NoMac, iOS (14,0)]
 	[BaseType (typeof (CPNowPlayingButton))]
-	interface CPNowPlayingRepeatButton {}
+	interface CPNowPlayingRepeatButton {
+		[Export ("initWithHandler:")]
+		NativeHandle Constructor ([NullAllowed] Action<CPNowPlayingButton> handler);
+	}
 
 	interface ICPListTemplateItem { }