Introduced new SetContentTypeDescriptors() overload

The initial overload of `SetContentTypeDescriptors()` (f1ade10) operated just like the `GetContentTypeDescriptors()` method it replaced in that it accepted a `ContentTypeDescriptor`—which it expected to be the _root_ `ContentTypeDescriptor` (i.e., `Root:Configuration:ContentTypes`) (b206f3e)

This overload provides a bit more flexibility by allowing a caller to submit _any_ `Topic`—not just a `ContentTypeDescriptor`—from _anywhere_ within the topic graph—not just `Root:Configuration:ContentTypes`. This is just a convenience method to make it really easy to update the content type configuration by passing in a reference to the topic graph via any node in that graph, and trusting it to find the node it relies on.

(This process is easy with the newish `GetByUniqueKey()` extension method, but it's still handy having it centralized, instead of needing to do that lookup each time it's called.)

Author: JeremyCaney

OnTopic/Repositories/TopicRepositoryBase.cs

@@ -112,6 +112,18 @@ protected virtual ContentTypeDescriptorCollection GetContentTypeDescriptors(Cont
     /*==========================================================================================================================
     | SET CONTENT TYPE DESCRIPTORS
     \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <summary>
+    ///   Allows for the content type descriptor cache to be (re)initialized based on an in-memory topic graph, by first
+    ///   identifying the root <see cref="ContentTypeDescriptor"/> from within the current content graph.
+    /// </summary>
+    /// <param name="sourceTopic">
+    ///   A <see cref="Topic"/> within the source topic graph. This overload will use this topic to identify the root <see cref=
+    ///   "ContentTypeDescriptor"/> within the graph.
+    /// </param>
+    /// <returns></returns>
+    protected virtual ContentTypeDescriptorCollection SetContentTypeDescriptors(Topic? sourceTopic) =>
+      SetContentTypeDescriptors(sourceTopic?.GetByUniqueKey("Root:Configuration:ContentTypes") as ContentTypeDescriptor);
+
     /// <summary>
     ///   Allows for the content type descriptor cache to be (re)initialized based on an in-memory topic graph, starting with
     ///   the root <see cref="ContentTypeDescriptor"/>.