NetCore: MSDI refactor split CoreRuntime & Remove Current (#9356)

* Split Bootstrap code from CoreRuntime

* Make ContentService method signatures match interface
prevents need to hide the concrete class in tests

* Remove Current

Only bit that bugs me is TreeNode for IconFilePath
I get the feeling it's dead code, but can just use a setter in cs or work out path in js if required.

* Fix tests, remember to terminate IRuntime

src/Umbraco.Web.Common/Controllers/UmbracoController.cs

@@ -2,7 +2,6 @@
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
-using Umbraco.Composing;
 using Umbraco.Core.Cache;
 using Umbraco.Core.Logging;
 using Umbraco.Core.Configuration.Models;