ThreadException only accepts one handler (#3108)

Cross-reference https://stackoverflow.com/q/57717007/3119991

Author: danAtAllworx

xml/System.Windows.Forms/Application.xml

@@ -1789,13 +1789,16 @@ The high DPI mode is set once per process. For more information about setting th
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 ## Remarks  
- This event allows your Windows Forms application to handle otherwise unhandled exceptions that occur in Windows Forms threads. Attach your event handlers to the <xref:System.Windows.Forms.Application.ThreadException> event to deal with these exceptions, which will leave your application in an unknown state. Where possible, exceptions should be handled by a structured exception handling block.  
+ This event allows your Windows Forms application to handle otherwise unhandled exceptions that occur in Windows Forms threads. Attach your event handler to the <xref:System.Windows.Forms.Application.ThreadException> event to deal with these exceptions, which will leave your application in an unknown state. Where possible, exceptions should be handled by a structured exception handling block.  
   
  You can change whether this callback is used for unhandled Windows Forms thread exceptions by setting <xref:System.Windows.Forms.Application.SetUnhandledExceptionMode%2A>. To catch exceptions that occur in threads not created and owned by Windows Forms, use the <xref:System.AppDomain.UnhandledException> event handler.  
   
 > [!NOTE]
 >  To guarantee that no activations of this event are missed, you must attach a handler before you call <xref:System.Windows.Application.Run%2A?displayProperty=nameWithType>.  
   
+> [!NOTE]
+>  Only one handler can be attached to this event. If multiple handlers are added, only the most recently added handler will be called on an unhandled exception.
+  
 > [!CAUTION]
 >  Because this is a static event, you must detach your event handlers when your application is disposed, or memory leaks will result.