Add a new feed dotnet-core

This is the *new* and most correct feed for our developer builds.
Leaving the old ones there for now because the other ASP.NET Repos also
left them there.

build/sources.props

@@ -5,6 +5,7 @@
     <RestoreSources>$(DotNetRestoreSources)</RestoreSources>
     <RestoreSources Condition="'$(DotNetBuildOffline)' != 'true' AND '$(AspNetUniverseBuildOffline)' != 'true' ">
       $(RestoreSources);
+      https://dotnet.myget.org/F/dotnet-core/api/v3/index.json;
       https://dotnet.myget.org/F/aspnetcore-dev/api/v3/index.json;
       https://dotnet.myget.org/F/aspnetcore-tools/api/v3/index.json
     </RestoreSources>

src/Microsoft.AspNetCore.Blazor.Razor.Extensions/BlazorConfiguration.cs

@@ -1,16 +0,0 @@
-// 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 System;
-using Microsoft.AspNetCore.Razor.Language;
-
-namespace Microsoft.AspNetCore.Blazor.Razor
-{
-    public static class BlazorConfiguration 
-    {
-        public static readonly RazorConfiguration Default = new RazorConfiguration(
-            RazorLanguageVersion.Version_2_1,
-            "Blazor-0.1",
-            Array.Empty<RazorExtension>());
-    }
-}

src/Microsoft.AspNetCore.Blazor.Razor.Extensions/BlazorExtensionInitializer.cs

@@ -17,30 +17,15 @@ namespace Microsoft.AspNetCore.Blazor.Razor
 
         static BlazorExtensionInitializer()
         {
-            // RazorConfiguration is changing between 15.7 and preview2 builds of Razor, this is a reflection-based
+            DeclarationConfiguration = RazorConfiguration.Create(
-            // workaround.
+                RazorLanguageVersion.Version_2_1, // Cannot use experimental until 15.7p4
-            DeclarationConfiguration = Create("BlazorDeclaration-0.1");
+                "BlazorDeclaration-0.1",
-            DefaultConfiguration = Create("Blazor-0.1");
+                Array.Empty<RazorExtension>());
 
-            RazorConfiguration Create(string configurationName)
+            DefaultConfiguration = RazorConfiguration.Create(
-            {
+                RazorLanguageVersion.Version_2_1,
-                var args = new object[] { RazorLanguageVersion.Version_2_1, configurationName, Array.Empty<RazorExtension>(), };
+                "Blazor-0.1",
-
+                Array.Empty<RazorExtension>());
-                MethodInfo method;
-                ConstructorInfo constructor;
-                if ((method = typeof(RazorConfiguration).GetMethod("Create", BindingFlags.Public | BindingFlags.Static)) != null)
-                {
-                    return (RazorConfiguration)method.Invoke(null, args);
-                }
-                else if ((constructor = typeof(RazorConfiguration).GetConstructors().FirstOrDefault()) != null)
-                {
-                    return (RazorConfiguration)constructor.Invoke(args);
-                }
-                else
-                {
-                    throw new InvalidOperationException("Can't create a configuration. This is bad.");
-                }
-            }
         }
 
         public static void Register(RazorProjectEngineBuilder builder)