cmdpal: fix a leak in the extension template (#39209)

There's apparently a footgun with the way we're using ComServer, which
results in us leaking the extension processes when we think we've
disposed them

The fix unfortunately has to be on the extension side. Extensions
published prior to 0.2 will need to manually fix this.

closes: #39045

src/modules/cmdpal/ExtensionTemplate/TemplateCmdPalExtension/TemplateCmdPalExtension/Program.cs

@@ -14,11 +14,12 @@ namespace TemplateCmdPalExtension;
 public class Program
 {
     [MTAThread]
-    public static async Task Main(string[] args)
+    public static void Main(string[] args)
     {
         if (args.Length > 0 && args[0] == "-RegisterProcessAsComServer")
         {
-            await using global::Shmuelie.WinRTServer.ComServer server = new();
+            global::Shmuelie.WinRTServer.ComServer server = new();
+
             ManualResetEvent extensionDisposedEvent = new(false);
             
             // We are instantiating an extension instance once above, and returning it every time the callback in RegisterExtension below is called.
@@ -31,6 +32,8 @@ public class Program
             // This will make the main thread wait until the event is signalled by the extension class.
             // Since we have single instance of the extension object, we exit as soon as it is disposed.
             extensionDisposedEvent.WaitOne();
+            server.Stop();
+            server.UnsafeDispose();
         }
         else
         {