Introduced MapTopicAreaRoute() overload for mapping all areas

The existing `MapTopicAreaRoute()` extension method recently introduced (6c6ad74) requires, at minimum, an `areaName` parameter, and thus is limited to setting up routes for one individual area at a time.

This extension doesn't (currently) accept any parameters, and will instead map _all_ areas to support the `{**path}` catch-all expected by the OnTopic CMS. It does this by implementing the new `TopicRouteValueTransformer` (865f26a) to automatically set the `controller` and the `rootTopic` routing variables to the `area` name, which is the convention we most frequently follow.

As part of this, I also registered `TopicRouteValueTransformer` with ASP.NET Core dependent injection, as part of the `AddTopicSupport()` extension.

Be aware that this implementation trips of a feature limitation of ASP.NET Core 3.0 which prevents e.g. `@Url.Action()` references from correctly returning values (see dotnet/aspnetcore#16965). Hopefully that will be resolved in ASP.NET 4.0.

Author: JeremyCaney

OnTopic.AspNetCore.Mvc/ServiceCollectionExtensions.cs

@@ -3,13 +3,15 @@
 | Client        Ignia, LLC
 | Project       Topics Library
 \=============================================================================================================================*/
-using OnTopic.AspNetCore.Mvc.Controllers;
-using OnTopic.Internal.Diagnostics;
+using System;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Mvc.Infrastructure;
+using Microsoft.AspNetCore.Mvc.TagHelpers;
 using Microsoft.AspNetCore.Routing;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.DependencyInjection.Extensions;
+using OnTopic.AspNetCore.Mvc.Controllers;
+using OnTopic.Internal.Diagnostics;
 
 namespace OnTopic.AspNetCore.Mvc {
 
@@ -38,6 +40,7 @@ public static IMvcBuilder AddTopicSupport(this IMvcBuilder services) {
       | Register services
       \-----------------------------------------------------------------------------------------------------------------------*/
       services.Services.TryAddSingleton<IActionResultExecutor<TopicViewResult>, TopicViewResultExecutor>();
+      services.Services.TryAddSingleton<TopicRouteValueTransformer>();
 
       /*------------------------------------------------------------------------------------------------------------------------
       | Configure services
@@ -127,6 +130,21 @@ public static ControllerActionEndpointConventionBuilder MapTopicAreaRoute(
         defaults: new { controller = controller?? areaName, action, rootTopic = areaName }
       );
 
+    /// <summary>
+    ///   Adds the <c>{area:exists}/{**path}</c> endpoint route for all areas, which enables the areas to be mapped to specific
+    ///   topics via the <see cref="TopicRepositoryExtensions.Load(Repositories.ITopicRepository, RouteData)"/> extension method
+    ///   used by <see cref="TopicController"/>.
+    /// </summary>
+    /// <remarks>
+    ///   Be aware that this method uses the <see cref="ControllerEndpointRouteBuilderExtensions.MapDynamicControllerRoute{
+    ///   TTransformer}(IEndpointRouteBuilder, String)"/> method. In .NET 3.x, this is incompatible with both the <see cref=
+    ///   "AnchorTagHelper"/> and <see cref="LinkGenerator"/> classes. This means that e.g. <c>@Url.Action()</c> references
+    ///   in views won't be properly formed. If these are required, prefer registering each route individually using <see cref=
+    ///   "MapTopicAreaRoute(IEndpointRouteBuilder, String, String?, String)"/>.
+    /// </remarks>
+    public static void MapTopicAreaRoute(this IEndpointRouteBuilder routes) =>
+      routes.MapDynamicControllerRoute<TopicRouteValueTransformer>("{area:exists}/{**path}");
+
     /*==========================================================================================================================
     | EXTENSION: MAP DEFAULT AREA CONTROLLER ROUTES (IENDPOINTROUTEBUILDER)
     \-------------------------------------------------------------------------------------------------------------------------*/