[dotnet] IJavascriptEngine implements IDisposable where available (#11594)

JavascriptExecutor takes an IWebDriver and, on a lazy basis, opens a
DevToolsSession which it currently leaves open. This PR disposes on
that DevToolsSession if it was instantiated.

Author: RenderMichael

dotnet/src/webdriver/IJavaScriptEngine.cs

@@ -25,7 +25,7 @@ namespace OpenQA.Selenium
     /// <summary>
     /// Defines an interface allowing the user to manage settings in the browser's JavaScript engine.
     /// </summary>
-    public interface IJavaScriptEngine
+    public interface IJavaScriptEngine : IDisposable
     {
         /// <summary>
         /// Occurs when a JavaScript callback with a named binding is executed.

dotnet/src/webdriver/JavaScriptEngine.cs

@@ -40,6 +40,7 @@ public class JavaScriptEngine : IJavaScriptEngine
         private Dictionary<string, PinnedScript> pinnedScripts = new Dictionary<string, PinnedScript>();
         private List<string> bindings = new List<string>();
         private bool isEnabled = false;
+        private bool isDisposed = false;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="JavaScriptEngine"/> class.
@@ -394,5 +395,26 @@ private void OnConsoleApiCalled(object sender, ConsoleApiCalledEventArgs e)
                 });
             }
         }
+
+        public void Dispose()
+        {
+            this.Dispose(true);
+        }
+
+        protected virtual void Dispose(bool disposing)
+        {
+            if (!this.isDisposed)
+            {
+                if (disposing)
+                {
+                    if (this.session.IsValueCreated)
+                    {
+                        this.session.Value.Dispose();
+                    }
+                }
+
+                this.isDisposed = true;
+            }
+        }
     }
 }