[Messages] Update to Xcode 26 beta 2-4. (#23470)

Author: rolfbjarne

src/messages.cs

@@ -97,6 +97,11 @@ interface MSMessagesAppTranscriptPresentation {
 		[Export ("messageTintColor")]
 		UIColor MessageTintColor { get; }
 
+		[iOS (26, 0), MacCatalyst (26, 0)]
+		[Abstract]
+		[Export ("messageCornerRadius")]
+		nfloat MessageCornerRadius { get; }
+
 		[iOS (26, 0), MacCatalyst (26, 0)]
 		[Abstract]
 		[Export ("invalidateMessageTintColor")]