Add empty event implementations for unused events.

src/Avalonia.DesignerSupport/Remote/DetachableTransportConnection.cs

@@ -30,6 +30,10 @@ namespace Avalonia.DesignerSupport.Remote
 
         public event Action<IAvaloniaRemoteTransportConnection, object> OnMessage;
 
-        public event Action<IAvaloniaRemoteTransportConnection, Exception> OnException;
+        public event Action<IAvaloniaRemoteTransportConnection, Exception> OnException
+        {
+            add {}
+            remove {}
+        }
     }
 }

src/Avalonia.DesignerSupport/Remote/PreviewerWindowImpl.cs

@@ -44,7 +44,11 @@ namespace Avalonia.DesignerSupport.Remote
         public WindowState WindowState { get; set; }
         public Action<WindowState> WindowStateChanged { get; set; }
         public Size MaxClientSize { get; } = new Size(4096, 4096);
-        public event Action LostFocus;
+        public event Action LostFocus
+        {
+            add {}
+            remove {}
+        }
 
         protected override void OnMessage(IAvaloniaRemoteTransportConnection transport, object obj)
         {

src/Avalonia.DesignerSupport/Remote/RemoteDesignerEntryPoint.cs

@@ -125,7 +125,11 @@ namespace Avalonia.DesignerSupport.Remote
 
         class NeverClose : ICloseable
         {
-            public event EventHandler Closed;
+            public event EventHandler Closed
+            {
+                add {}
+                remove {}
+            }
         }
         
         public static void Main(string[] cmdline)

src/Markup/Avalonia.Markup.Xaml/Styling/StyleInclude.cs

@@ -26,7 +26,11 @@ namespace Avalonia.Markup.Xaml.Styling
         }
 
         /// <inheritdoc/>
-        public event EventHandler<ResourcesChangedEventArgs> ResourcesChanged;
+        public event EventHandler<ResourcesChangedEventArgs> ResourcesChanged
+        {
+            add {}
+            remove {}
+        }
 
         /// <summary>
         /// Gets or sets the source URL.

src/iOS/Avalonia.iOS/EmbeddableImpl.cs

@@ -27,6 +27,10 @@ namespace Avalonia.iOS
         {
         }
 
-        public event Action LostFocus;
+        public event Action LostFocus
+        {
+            add {}
+            remove {}
+        }
     }
 }