Use string instead of String (#4602)

* Use string instead of String

* Update Form1.cs

* Re-trigger build

Author: Youssef1313

samples/snippets/csharp/VS_Snippets_Winforms/System.ComponentModel.IPropertyChangeExample/CS/Form1.cs

@@ -81,15 +81,15 @@ public class DemoCustomer : INotifyPropertyChanged
     {
         // These fields hold the values for the public properties.
         private Guid idValue = Guid.NewGuid();
-        private string customerNameValue = String.Empty;
-        private string phoneNumberValue = String.Empty;
+        private string customerNameValue = string.Empty;
+        private string phoneNumberValue = string.Empty;
 
         public event PropertyChangedEventHandler PropertyChanged;
 
         // This method is called by the Set accessor of each property.
         // The CallerMemberName attribute that is applied to the optional propertyName
         // parameter causes the property name of the caller to be substituted as an argument.
-        private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
+        private void NotifyPropertyChanged([CallerMemberName] string propertyName = "")
         {
             if (PropertyChanged != null)
             {
@@ -156,4 +156,4 @@ public string PhoneNumber
     }
     // </snippet9>
 }
-// </snippet1>
+// </snippet1>