.NET: [BREAKING] Propagate CancellationToken into Workflow Executors and message handlers (#1280)

* feat: Propagate CancellationToken to Executors

* Also adds cancellation propagation to `Executor`-accessible APIs
* Adds registrators for cancellable handlers to `RouteBuilder`
* [BREAKING]: Adds `CancellationToken` to `IMessageHandler.HandleAsync`

* test: Re-enable Concurrent Orchestration test

* refactor: Delete unused IInputCoordinator

* refactor: Remove superfluous argument qualifications

dotnet/samples/GettingStarted/Workflows/Observability/ApplicationInsights/Program.cs

@@ -76,8 +76,10 @@ internal sealed class UppercaseExecutor() : ReflectingExecutor<UppercaseExecutor
     /// </summary>
     /// <param name="message">The input text to convert</param>
     /// <param name="context">Workflow context for accessing workflow services and adding events</param>
+    /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests.
+    /// The default is <see cref="CancellationToken.None"/>.</param>
     /// <returns>The input text converted to uppercase</returns>
-    public async ValueTask<string> HandleAsync(string message, IWorkflowContext context) =>
+    public async ValueTask<string> HandleAsync(string message, IWorkflowContext context, CancellationToken cancellationToken = default) =>
         message.ToUpperInvariant(); // The return value will be sent as a message along an edge to subsequent executors
 }
 
@@ -91,6 +93,9 @@ internal sealed class ReverseTextExecutor() : ReflectingExecutor<ReverseTextExec
     /// </summary>
     /// <param name="message">The input text to reverse</param>
     /// <param name="context">Workflow context for accessing workflow services and adding events</param>
+    /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests.
+    /// The default is <see cref="CancellationToken.None"/>.</param>
     /// <returns>The input text reversed</returns>
-    public async ValueTask<string> HandleAsync(string message, IWorkflowContext context) => new string(message.Reverse().ToArray());
+    public async ValueTask<string> HandleAsync(string message, IWorkflowContext context, CancellationToken cancellationToken = default)
+        => new(message.Reverse().ToArray());
 }