Add UseReactDevelopmentServer() middleware. Factor out common code.

src/Microsoft.AspNetCore.SpaServices.Extensions/Util/LoggerFinder.cs

@@ -0,0 +1,25 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.AspNetCore.Builder;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Logging.Console;
+
+namespace Microsoft.AspNetCore.SpaServices.Util
+{
+    internal static class LoggerFinder
+    {
+        public static ILogger GetOrCreateLogger(
+            IApplicationBuilder appBuilder,
+            string logCategoryName)
+        {
+            // If the DI system gives us a logger, use it. Otherwise, set up a default one.
+            var loggerFactory = appBuilder.ApplicationServices.GetService<ILoggerFactory>();
+            var logger = loggerFactory != null
+                ? loggerFactory.CreateLogger(logCategoryName)
+                : new ConsoleLogger(logCategoryName, null, false);
+            return logger;
+        }
+    }
+}