Introduced AttributeDictionary constructor for relationships

The `RelationshipAttributeDescriptorViewModel` was inadvertently missed when originally implementing the `AttributeDictionary` constructor overloads on the `AttributeDescriptorViewModel` implementations (7e15db9). This doesn't _harm_ anything, but it also prevents this particular attribute from taking advantage of the performance benefits of the `AttributeDictionary` constructor.

Author: JeremyCaney

OnTopic.Editor.AspNetCore.Attributes/RelationshipAttribute/RelationshipAttributeDescriptorViewModel.cs

@@ -18,10 +18,33 @@ public record RelationshipAttributeDescriptorViewModel: QueryableTopicListAttrib
     /*==========================================================================================================================
     | CONSTRUCTOR
     \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <summary>
+    ///   Initializes a new <see cref="RelationshipAttributeDescriptorViewModel"/> with an <paramref name="attributes"/> dictionary.
+    /// </summary>
+    /// <param name="attributes">An <see cref="AttributeDictionary"/> of attribute values.</param>
+    public RelationshipAttributeDescriptorViewModel(AttributeDictionary attributes): base(attributes) {
+      Contract.Requires(attributes, nameof(attributes));
+      ShowRoot                  = attributes.GetBoolean(nameof(ShowRoot));
+      ExpandRelated             = attributes.GetBoolean(nameof(ExpandRelated));
+      CheckAscendants           = attributes.GetBoolean(nameof(CheckAscendants));
+      RegisterResources();
+    }
+
     /// <summary>
     ///   Initializes a new instance of a <see cref="RelationshipAttributeDescriptorViewModel"/>
     /// </summary>
     public RelationshipAttributeDescriptorViewModel() {
+      RegisterResources();
+    }
+
+    /*==========================================================================================================================
+    | REGISTER RESOURCES
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <summary>
+    ///   Derived classes may optionally override this method in order to register resources, as an alternative to setting these
+    ///   in the constructor.
+    /// </summary>
+    protected void RegisterResources() {
       Scripts.Register(GetNamespacedUri("/Shared/Scripts/SelectableTreeView.js"));
     }