API Change - IJavascriptObjectRepository.Register remove isAsync default param

**BREAKING CHANGE**

- You must now explicitly specify the `isAsync` param.
- Add additional xml doc comment regarding .Net Core and using only isAsync = true

The isAsync = false option (sync binding) requires WCF which isn't available on .Net core, remove the default value so you are forced to specify an option and in the process hopefully read the documentation.

For those who previously hadn't provided a param then simply pass in false for the third argument.
e.g.
browser.JavascriptObjectRepository.Register("bound", new BoundObject(), false);

Resolves #3016

Author: amaitland

CefSharp.WinForms.Example/Minimal/SimpleBrowserForm.cs

@@ -6,7 +6,6 @@
 using System.ComponentModel;
 using System.Windows.Forms;
 using CefSharp.Example.JavascriptBinding;
-using CefSharp.WinForms.Internals;
 
 namespace CefSharp.WinForms.Example.Minimal
 {
@@ -68,7 +67,7 @@ private void CreateBrowser()
             browser.StatusMessage += OnBrowserStatusMessage;
             browser.TitleChanged += OnBrowserTitleChanged;
             browser.AddressChanged += OnBrowserAddressChanged;
-            browser.JavascriptObjectRepository.Register("bound", new BoundObject());
+            browser.JavascriptObjectRepository.Register("bound", new BoundObject(), false);
             if (!multiThreadedMessageLoop)
             {
                 browser.FocusHandler = null;

CefSharp.Wpf.Example/JavascriptCallbackMainWindow.xaml.cs

@@ -19,8 +19,8 @@ public JavascriptCallbackMainWindow()
             boundObjectOne = new JavascriptCallbackBoundObject(BrowserOne);
             boundObjectTwo = new JavascriptCallbackBoundObject(BrowserTwo);
 
-            BrowserOne.JavascriptObjectRepository.Register("boundObject", boundObjectOne);
-            BrowserTwo.JavascriptObjectRepository.Register("boundObject", boundObjectTwo);
+            BrowserOne.JavascriptObjectRepository.Register("boundObject", boundObjectOne, false);
+            BrowserTwo.JavascriptObjectRepository.Register("boundObject", boundObjectTwo, false);
         }
 
         private void ExecuteCallbackImmediatelyClick(object sender, RoutedEventArgs e)

CefSharp/IJavascriptObjectRepository.cs

@@ -30,10 +30,11 @@ public interface IJavascriptObjectRepository : IDisposable
         /// only methods will be exposed and when called from javascript will return a Promise to be awaited. 
         /// This method is newer and recommended for everyone starting out as it is faster and more reliable.
         /// If false then methods and properties will be registered, this method relies on a WCF service to communicate.
+        /// If you are targeting .Net Core then you can only use isAsync = true as Microsoft has chosen not to support WCF.
         /// </param>
         /// <param name="options">binding options, by default method/property names are camelCased, you can control this
         /// and other advanced options though this class.</param>
-        void Register(string name, object objectToBind, bool isAsync = false, BindingOptions options = null);
+        void Register(string name, object objectToBind, bool isAsync, BindingOptions options = null);
         /// <summary>
         /// UnRegister all the currently bound objects from the repository. If you unregister an object that is currently
         /// bound in JavaScript then the method/property calls will fail.