fix #11114 by setting DesignerCategory for WebHostService (#11123)

src/Hosting/WindowsServices/ref/Microsoft.AspNetCore.Hosting.WindowsServices.netcoreapp3.0.cs

@@ -3,6 +3,7 @@
 
 namespace Microsoft.AspNetCore.Hosting.WindowsServices
 {
+    [System.ComponentModel.DesignerCategoryAttribute("Code")]
     public partial class WebHostService : System.ServiceProcess.ServiceBase
     {
         public WebHostService(Microsoft.AspNetCore.Hosting.IWebHost host) { }

src/Hosting/WindowsServices/src/WebHostService.cs

@@ -12,6 +12,7 @@ namespace Microsoft.AspNetCore.Hosting.WindowsServices
     /// <summary>
     ///     Provides an implementation of a Windows service that hosts ASP.NET Core.
     /// </summary>
+    [DesignerCategory("Code")]
     public class WebHostService : ServiceBase
     {
         private readonly IWebHost _host;