Ensured Value and InheritedValue were wired up

Resolves `IDE0060`. We optionally allow `Value` and `InheritedValue` to be defined via the constructor of an `AttributeViewModel<T>` or any derived classes. That makes some sense, given that these are the most likely values to be defined on the view model. That said, these weren't actually wired up, which is a recipe for confusion. In practice, we might consider removing these since the editor itself doesn't actually utilize these, but removing them will require updating each of the derived classes (which also relay these). Technically, it would also break the public interface since these are all marked as `public`. (The only reason they're marked as `public`, though, is because they're part of a separate project for organizational purposes; that's an organizational decision we will want to revisit in the next major release.)

Author: JeremyCaney

OnTopic.Editor.Models/AttributeViewModel{T}.cs

@@ -31,7 +31,9 @@ public AttributeViewModel(
       currentTopic,
       attributeDescriptor
     ) {
-      AttributeDescriptor = attributeDescriptor;
+      AttributeDescriptor       = attributeDescriptor;
+      Value                     = value;
+      InheritedValue            = inheritedValue;
     }
 
     /*==========================================================================================================================