[Components] Prerrendering startup experience (#7770)

[Components] Prerrendering startup experience
* Introduces an IComponentPrerrenderer to handle Prerrendering
  * MVC registers a basic static prerrrenderer.
  * Components registers a more feature complete prerrender that will
    handle reconnection to the original circuit after prerrendering in
    the future to allow for prerrendered interactive components.
* Removes UseRazorComponents
  * Removes the SPA fallback in favor of a catch all route in
    Index.cshtml
  * Moves the framework files to be served by the default StaticFiles
    middleware in the pipeline by way of plugging specific providers
    through options.
  * Lifts UseSignalR(r => r.MapHub<ComponentHub>()) into startup and
    replaces it with a shorthand for MapHub using endpoint routing.
  * Adds extension methods to map components to selectors for a given
    hub.
* Updates the razor component templates to include prerendering and use a razor page as the entry 
   point.

Author: javiercn

src/Components/Server/src/Builder/ComponentEndpointConventionBuilderExtensions.cs

@@ -0,0 +1,75 @@
+// 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 System.Collections.Generic;
+using Microsoft.AspNetCore.Components.Server;
+
+namespace Microsoft.AspNetCore.Builder
+{
+    /// <summary>
+    /// Extensions for <see cref="IEndpointConventionBuilder"/>.
+    /// </summary>
+    public static class ComponentEndpointConventionBuilderExtensions
+    {
+        /// <summary>
+        /// Adds <typeparamref name="TComponent"/> to the list of components registered with this <see cref="ComponentHub"/> instance.
+        /// </summary>
+        /// <typeparam name="TComponent">The component type.</typeparam>
+        /// <param name="builder">The <see cref="IEndpointConventionBuilder"/>.</param>
+        /// <param name="selector">A CSS selector that identifies the DOM element into which the <typeparamref name="TComponent"/> will be placed.</param>
+        /// <returns>The <paramref name="builder"/>.</returns>
+        public static IEndpointConventionBuilder AddComponent<TComponent>(this IEndpointConventionBuilder builder, string selector)
+        {
+            if (builder == null)
+            {
+                throw new ArgumentNullException(nameof(builder));
+            }
+
+            if (selector == null)
+            {
+                throw new ArgumentNullException(nameof(selector));
+            }
+
+            return AddComponent(builder, typeof(TComponent), selector);
+        }
+
+        /// <summary>
+        /// Adds <paramref name="componentType"/> to the list of components registered with this <see cref="ComponentHub"/> instance.
+        /// The selector will default to the component name in lowercase.
+        /// </summary>
+        /// <param name="builder">The <see cref="IEndpointConventionBuilder"/>.</param>
+        /// <param name="componentType">The component type.</param>
+        /// <param name="selector">The component selector in the DOM for the <paramref name="componentType"/>.</param>
+        /// <returns>The <paramref name="builder"/>.</returns>
+        public static IEndpointConventionBuilder AddComponent(this IEndpointConventionBuilder builder, Type componentType, string selector)
+        {
+            if (builder == null)
+            {
+                throw new ArgumentNullException(nameof(builder));
+            }
+
+            if (componentType == null)
+            {
+                throw new ArgumentNullException(nameof(componentType));
+            }
+
+            if (selector == null)
+            {
+                throw new ArgumentNullException(nameof(selector));
+            }
+
+            builder.Add(endpointBuilder => AddComponent(endpointBuilder.Metadata, componentType, selector));
+            return builder;
+        }
+
+        private static void AddComponent(IList<object> metadata, Type type, string selector)
+        {
+            metadata.Add(new ComponentDescriptor
+            {
+                ComponentType = type,
+                Selector = selector
+            });
+        }
+    }
+}

src/Components/Server/src/Builder/ComponentEndpointRouteBuilderExtensions.cs

@@ -0,0 +1,110 @@
+// 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.Components.Server;
+using Microsoft.AspNetCore.Routing;
+
+namespace Microsoft.AspNetCore.Builder
+{
+    /// <summary>
+    /// Extensions for <see cref="IEndpointRouteBuilder"/>.
+    /// </summary>
+    public static class ComponentEndpointRouteBuilderExtensions
+    {
+        /// <summary>
+        /// Maps the SignalR <see cref="ComponentHub"/> to the path <paramref name="path"/> and associates
+        /// the component <typeparamref name="TComponent"/> to this hub instance as the given DOM <paramref name="selector"/>.
+        /// </summary>
+        /// <typeparam name="TComponent">The first <see cref="IComponent"/> associated with this <see cref="ComponentHub"/>.</typeparam>
+        /// <param name="routes">The <see cref="RouteBuilder"/>.</param>
+        /// <param name="selector">The selector for the <typeparamref name="TComponent"/>.</param>
+        /// <returns>The <see cref="IEndpointConventionBuilder"/>.</returns>
+        public static IEndpointConventionBuilder MapComponentHub<TComponent>(
+            this IEndpointRouteBuilder routes,
+            string selector)
+        {
+            if (routes == null)
+            {
+                throw new ArgumentNullException(nameof(routes));
+            }
+
+            if (selector == null)
+            {
+                throw new ArgumentNullException(nameof(selector));
+            }
+
+            return routes.MapComponentHub(typeof(TComponent), selector, ComponentHub.DefaultPath);
+        }
+
+        /// <summary>
+        /// Maps the SignalR <see cref="ComponentHub"/> to the path <paramref name="path"/> and associates
+        /// the component <typeparamref name="TComponent"/> to this hub instance as the given DOM <paramref name="selector"/>.
+        /// </summary>
+        /// <typeparam name="TComponent">The first <see cref="IComponent"/> associated with this <see cref="ComponentHub"/>.</typeparam>
+        /// <param name="routes">The <see cref="RouteBuilder"/>.</param>
+        /// <param name="selector">The selector for the <typeparamref name="TComponent"/>.</param>
+        /// <param name="path">The path to map to which the <see cref="ComponentHub"/> will be mapped.</param>
+        /// <returns>The <see cref="IEndpointConventionBuilder"/>.</returns>
+        public static IEndpointConventionBuilder MapComponentHub<TComponent>(
+            this IEndpointRouteBuilder routes,
+            string selector,
+            string path)
+        {
+            if (routes == null)
+            {
+                throw new ArgumentNullException(nameof(routes));
+            }
+
+            if (path == null)
+            {
+                throw new ArgumentNullException(nameof(path));
+            }
+
+            if (selector == null)
+            {
+                throw new ArgumentNullException(nameof(selector));
+            }
+
+            return routes.MapComponentHub(typeof(TComponent), selector, path);
+        }
+
+        /// <summary>
+        /// Maps the SignalR <see cref="ComponentHub"/> to the path <paramref name="path"/> and associates
+        /// the component <paramref name="componentType"/> to this hub instance as the given DOM <paramref name="selector"/>.
+        /// </summary>
+        /// <param name="routes">The <see cref="RouteBuilder"/>.</param>
+        /// <param name="componentType">The first <see cref="IComponent"/> associated with this <see cref="ComponentHub"/>.</param>
+        /// <param name="selector">The selector for the <paramref name="componentType"/>.</param>
+        /// <param name="path">The path to map to which the <see cref="ComponentHub"/> will be mapped.</param>
+        /// <returns>The <see cref="IEndpointConventionBuilder"/>.</returns>
+        public static IEndpointConventionBuilder MapComponentHub(
+            this IEndpointRouteBuilder routes,
+            Type componentType,
+            string selector,
+            string path)
+        {
+            if (routes == null)
+            {
+                throw new ArgumentNullException(nameof(routes));
+            }
+
+            if (path == null)
+            {
+                throw new ArgumentNullException(nameof(path));
+            }
+
+            if (componentType == null)
+            {
+                throw new ArgumentNullException(nameof(componentType));
+            }
+
+            if (selector == null)
+            {
+                throw new ArgumentNullException(nameof(selector));
+            }
+
+            return routes.MapHub<ComponentHub>(path).AddComponent(componentType, selector);
+        }
+    }
+}

src/Components/Server/src/Builder/RazorComponentsApplicationBuilderExtensions.cs

@@ -8,6 +8,10 @@ namespace Microsoft.AspNetCore.Components.Server.Circuits
 {
     internal abstract class CircuitFactory
     {
-        public abstract CircuitHost CreateCircuitHost(HttpContext httpContext, IClientProxy client);
+        public abstract CircuitHost CreateCircuitHost(
+            HttpContext httpContext,
+            IClientProxy client,
+            string uriAbsolute,
+            string baseUriAbsolute);
     }
 }