Add StringSyntax to the RouteAttribute (#57369)

I noticed when using the `[Route("/orders/{orderId:int}")]` attribute, as an example, doesn't display the same as when using the `EndpointRouteBuilderExtensions` APIs for `Map*` that accept a template/pattern. I think it would be great if we could also highlight routes when using the attribute. This PR adds the `StringSyntax` to decorate the `template` parameter to be highlighted like the method APIs.

Author: IEvangelist

src/Components/Components/src/RouteAttribute.cs

@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace Microsoft.AspNetCore.Components;
 
 /// <summary>
@@ -13,7 +15,7 @@ public sealed class RouteAttribute : Attribute
     /// Constructs an instance of <see cref="RouteAttribute"/>.
     /// </summary>
     /// <param name="template">The route template.</param>
-    public RouteAttribute(string template)
+    public RouteAttribute([StringSyntax("Route")] string template)
     {
         ArgumentNullException.ThrowIfNull(template);