Add the name of the current type to the exception we throw in an unsupported case.

src/Workspaces/Core/Portable/CodeActions/CodeAction.cs

@@ -170,7 +170,7 @@ protected virtual Task<IEnumerable<CodeActionOperation>> ComputePreviewOperation
         /// </remarks>
         /// <exception cref="NotSupportedException">If this code action does not support changing a single document.</exception>
         protected virtual Task<Document> GetChangedDocumentAsync(CancellationToken cancellationToken)
-            => throw new NotSupportedException();
+            => throw new NotSupportedException(GetType().FullName);
 
         /// <summary>
         /// used by batch fixer engine to get new solution