Service refactoring to "fully" enable segments (#19114)

* Refactor serverside content editing to support all variance combinations

* Fix build errors

* Reintroduce the tests ignored by #19060

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Co-authored-by: Mads Rasmussen <madsr@hey.com>

tests/Umbraco.Tests.Integration/Umbraco.Core/Services/DocumentNavigationServiceTestsBase.cs

@@ -49,7 +49,7 @@ internal abstract class DocumentNavigationServiceTestsBase : UmbracoIntegrationT
         {
             ContentTypeKey = contentTypeKey ?? ContentType.Key,
             ParentKey = parentKey ?? Constants.System.RootKey,
-            InvariantName = name,
+            Variants = [new () { Name = name }],
             Key = key,
         };