Rework of Blazor startup experience

Fixes: #16874

This is a significant simplication of our startup code model for Blazor
wasm with the goal of removing concepts that don't make much sense here.
Previously in this area we've tried to be consistent with ASP.NET Core
on the server, but it's not helping up much in WASM.

We're still leveraging some of the lessons from server-size ASP.NET
(hello CreateDefaultBuilder) but consistency is no longer a goal.

This change actually makes a bunch of scenarios better (rather than
removing features) - it's now possible to access services from the
application's DI scope and initialize them before the UI is shown
`RunAsync`.

This change also adds configuration in a central way. There's nothing in
this change that populates configuration in an automatic way, that will
come next.

Author: rynowak

src/Components/Blazor/Blazor/ref/Microsoft.AspNetCore.Blazor.csproj

@@ -7,6 +7,6 @@
     <Compile Include="Microsoft.AspNetCore.Blazor.netstandard2.1.cs" />
     <Reference Include="Mono.WebAssembly.Interop"  />
     <Reference Include="Microsoft.AspNetCore.Components.Web"  />
-    <Reference Include="Microsoft.Extensions.Options"  />
+    <Reference Include="Microsoft.Extensions.Configuration"  />
   </ItemGroup>
 </Project>

src/Components/Blazor/Blazor/ref/Microsoft.AspNetCore.Blazor.netstandard2.1.cs

@@ -12,38 +12,38 @@ public static void NotifyLocationChanged(string uri, bool isInterceptedLink) { }
 }
 namespace Microsoft.AspNetCore.Blazor.Hosting
 {
-    public static partial class BlazorWebAssemblyHost
+    [System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential)]
+    public readonly partial struct RootComponentMapping
     {
-        public static Microsoft.AspNetCore.Blazor.Hosting.IWebAssemblyHostBuilder CreateDefaultBuilder() { throw null; }
+        private readonly object _dummy;
+        public RootComponentMapping(System.Type componentType, string selector) { throw null; }
+        public System.Type ComponentType { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
+        public string Selector { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
     }
-    public partial interface IWebAssemblyHost : System.IDisposable
+    public partial class RootComponentMappingCollection : System.Collections.ObjectModel.Collection<Microsoft.AspNetCore.Blazor.Hosting.RootComponentMapping>
     {
-        System.IServiceProvider Services { get; }
-        System.Threading.Tasks.Task StartAsync(System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken));
-        System.Threading.Tasks.Task StopAsync(System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken));
+        public RootComponentMappingCollection() { }
+        public void Add(System.Type componentType, string selector) { }
+        public void AddRange(System.Collections.Generic.IEnumerable<Microsoft.AspNetCore.Blazor.Hosting.RootComponentMapping> items) { }
+        public void Add<TComponent>(string selector) where TComponent : Microsoft.AspNetCore.Components.IComponent { }
     }
-    public partial interface IWebAssemblyHostBuilder
+    public sealed partial class WebAssemblyHost : System.IAsyncDisposable
     {
-        System.Collections.Generic.IDictionary<object, object> Properties { get; }
-        Microsoft.AspNetCore.Blazor.Hosting.IWebAssemblyHost Build();
-        Microsoft.AspNetCore.Blazor.Hosting.IWebAssemblyHostBuilder ConfigureServices(System.Action<Microsoft.AspNetCore.Blazor.Hosting.WebAssemblyHostBuilderContext, Microsoft.Extensions.DependencyInjection.IServiceCollection> configureDelegate);
-        Microsoft.AspNetCore.Blazor.Hosting.IWebAssemblyHostBuilder UseServiceProviderFactory<TContainerBuilder>(Microsoft.Extensions.DependencyInjection.IServiceProviderFactory<TContainerBuilder> factory);
-        Microsoft.AspNetCore.Blazor.Hosting.IWebAssemblyHostBuilder UseServiceProviderFactory<TContainerBuilder>(System.Func<Microsoft.AspNetCore.Blazor.Hosting.WebAssemblyHostBuilderContext, Microsoft.Extensions.DependencyInjection.IServiceProviderFactory<TContainerBuilder>> factory);
+        internal WebAssemblyHost() { }
+        public Microsoft.Extensions.Configuration.IConfiguration Configuration { get { throw null; } }
+        public System.IServiceProvider Services { get { throw null; } }
+        [System.Diagnostics.DebuggerStepThroughAttribute]
+        public System.Threading.Tasks.ValueTask DisposeAsync() { throw null; }
+        public System.Threading.Tasks.Task RunAsync() { throw null; }
     }
-    public sealed partial class WebAssemblyHostBuilderContext
+    public sealed partial class WebAssemblyHostBuilder
     {
-        public WebAssemblyHostBuilderContext(System.Collections.Generic.IDictionary<object, object> properties) { }
-        public System.Collections.Generic.IDictionary<object, object> Properties { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
-    }
-    public static partial class WebAssemblyHostBuilderExtensions
-    {
-        public static Microsoft.AspNetCore.Blazor.Hosting.IWebAssemblyHostBuilder ConfigureServices(this Microsoft.AspNetCore.Blazor.Hosting.IWebAssemblyHostBuilder hostBuilder, System.Action<Microsoft.Extensions.DependencyInjection.IServiceCollection> configureDelegate) { throw null; }
-        public static Microsoft.AspNetCore.Blazor.Hosting.IWebAssemblyHostBuilder UseBlazorStartup(this Microsoft.AspNetCore.Blazor.Hosting.IWebAssemblyHostBuilder builder, System.Type startupType) { throw null; }
-        public static Microsoft.AspNetCore.Blazor.Hosting.IWebAssemblyHostBuilder UseBlazorStartup<TStartup>(this Microsoft.AspNetCore.Blazor.Hosting.IWebAssemblyHostBuilder builder) { throw null; }
-    }
-    public static partial class WebAssemblyHostExtensions
-    {
-        public static void Run(this Microsoft.AspNetCore.Blazor.Hosting.IWebAssemblyHost host) { }
+        internal WebAssemblyHostBuilder() { }
+        public Microsoft.Extensions.Configuration.IConfigurationBuilder Configuration { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
+        public Microsoft.AspNetCore.Blazor.Hosting.RootComponentMappingCollection RootComponents { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
+        public Microsoft.Extensions.DependencyInjection.IServiceCollection Services { [System.Runtime.CompilerServices.CompilerGeneratedAttribute]get { throw null; } }
+        public Microsoft.AspNetCore.Blazor.Hosting.WebAssemblyHost Build() { throw null; }
+        public static Microsoft.AspNetCore.Blazor.Hosting.WebAssemblyHostBuilder CreateDefault(string[] args = null) { throw null; }
     }
 }
 namespace Microsoft.AspNetCore.Blazor.Http
@@ -67,15 +67,3 @@ public static partial class WebAssemblyEventDispatcher
         public static System.Threading.Tasks.Task DispatchEvent(Microsoft.AspNetCore.Components.RenderTree.WebEventDescriptor eventDescriptor, string eventArgsJson) { throw null; }
     }
 }
-namespace Microsoft.AspNetCore.Components.Builder
-{
-    public static partial class ComponentsApplicationBuilderExtensions
-    {
-        public static void AddComponent<TComponent>(this Microsoft.AspNetCore.Components.Builder.IComponentsApplicationBuilder app, string domElementSelector) where TComponent : Microsoft.AspNetCore.Components.IComponent { }
-    }
-    public partial interface IComponentsApplicationBuilder
-    {
-        System.IServiceProvider Services { get; }
-        void AddComponent(System.Type componentType, string domElementSelector);
-    }
-}