.NET: [BREAKING] Workflows API Review Naming Changes (Part 1?) (#4090)

* refactor: Normalize Run/RunStreaming with AIAgent

* refactor: Clarify Session vs. Run -level concepts

* Rename RunId to SessionId to better match Run/Session terminology in AIAgent
* [BREAKING]: Will break existing checkpointed sessions in CosmosDb due to field rename

* refactor: Rename and simplify interface around getting typed data out of ExternalRequest/Response

* Also adds hints around using value types in PortableValue

* refactor: Rename AddFanInEdge to AddFanInBarrierEdge

This will prevent a breaking change later when we introduce a programmable FanIn edge, analogous to the FanOut edge's EdgeSelector.

The goal, in the long run is to support a number of different FanIn scenarios, with naive FanIn (no barrier) by default, similar to FanOut.

* refactor: AsAgent(this Workflow, ...) => AsAIAgent(...)

* misc - part1: SwitchBuilder internal

---------

Co-authored-by: Dmytro Struk <13853051+dmytrostruk@users.noreply.github.com>

dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowHostingExtensions.cs

@@ -25,7 +25,7 @@ public static class WorkflowHostingExtensions
     /// <param name="includeWorkflowOutputsInResponse">If <see langword="true"/>, will transform outgoing workflow outputs
     /// into into content in <see cref="AgentResponseUpdate"/>s or the <see cref="AgentResponse"/> as appropriate.</param>
     /// <returns></returns>
-    public static AIAgent AsAgent(
+    public static AIAgent AsAIAgent(
         this Workflow workflow,
         string? id = null,
         string? name = null,