Netcore: Turn container validation back on (#9401)

* Remove RuntimeLevelAttribute & disable filtering

* Remove RuntimeLevelAttribute usage on Composers

* Fix broken tests

* Resolve UserManager registration issues.

* Turn container validation back on.

* Resolve lifetime issue post install backoffice.

* Remove final TODO: MSDI

src/Umbraco.Web.UI.NetCore/Program.cs

@@ -21,9 +21,6 @@ namespace Umbraco.Web.UI.NetCore
                     x.ClearProviders();
                 })
                 .ConfigureWebHostDefaults(webBuilder => { webBuilder.UseStartup<Startup>(); })
-                // TODO: MSDI - this should probably be on one day
-                // First we need to resolve the composition conditional registration issues see #8563
-                .UseDefaultServiceProvider(options => options.ValidateOnBuild = false)
                 .UseUmbraco();
     }
 }