WPF - Use WPF specific menu handler by default

Resolves #1767

Author: amaitland

CefSharp.Wpf/ChromiumWebBrowser.cs

@@ -17,6 +17,7 @@
 using CefSharp.Internals;
 using CefSharp.Structs;
 using CefSharp.Wpf.Experimental;
+using CefSharp.Wpf.Handler;
 using CefSharp.Wpf.Internals;
 using CefSharp.Wpf.Rendering;
 using Microsoft.Win32.SafeHandles;
@@ -563,6 +564,8 @@ private void NoInliningConstructor()
 
             PresentationSource.AddSourceChangedHandler(this, PresentationSourceChangedHandler);
 
+            MenuHandler = new ContextMenuHandler();
+
             UseLayoutRounding = true;
         }