.NET: [BREAKING] refactor: Normalize WorkflowBuilder APIs (#1935)

* [BREAKING] refactor: Normalize WorkflowBuilder APIs

* "partitioner" => "assigner"
* normalize ordering so sources always to the left of targets for edges
* normalize parameter ordering so sources and targets are always first arguments
* remove `params` (users should use collection expressions instead)

* refactor: Align name with Python

dotnet/samples/GettingStarted/Workflows/ConditionalEdges/03_MultiSelection/Program.cs

@@ -60,13 +60,13 @@ public static class Program
         WorkflowBuilder builder = new(emailAnalysisExecutor);
         builder.AddFanOutEdge(
             emailAnalysisExecutor,
-            targets: [
+            [
                 handleSpamExecutor,
                 emailAssistantExecutor,
                 emailSummaryExecutor,
                 handleUncertainExecutor,
             ],
-            partitioner: GetPartitioner()
+            GetTargetAssigner()
         )
         // After the email assistant writes a response, it will be sent to the send email executor
         .AddEdge(emailAssistantExecutor, sendEmailExecutor)
@@ -105,7 +105,7 @@ public static class Program
     /// Creates a partitioner for routing messages based on the analysis result.
     /// </summary>
     /// <returns>A function that takes an analysis result and returns the target partitions.</returns>
-    private static Func<AnalysisResult?, int, IEnumerable<int>> GetPartitioner()
+    private static Func<AnalysisResult?, int, IEnumerable<int>> GetTargetAssigner()
     {
         return (analysisResult, targetCount) =>
         {