Add foundation

Toolkit.Foundation/IObservableViewModel.cs

@@ -0,0 +1,13 @@
+namespace Toolkit.Foundation;
+
+public interface IObservableViewModel :
+    IDisposable
+{
+    public IDisposer Disposer { get; }
+
+    public IPublisher Publisher { get; }
+
+    public IServiceFactory ServiceFactory { get; }
+
+    public IServiceProvider ServiceProvider { get; }
+}