Create new top-level DefaultNodeInstance concept that will soon hold the "connection draining" logic

src/Microsoft.AspNetCore.NodeServices/INodeServices.cs

@@ -0,0 +1,18 @@
+using System;
+using System.Threading.Tasks;
+
+namespace Microsoft.AspNetCore.NodeServices
+{
+    public interface INodeServices : IDisposable
+    {
+        Task<T> InvokeAsync<T>(string moduleName, params object[] args);
+
+        Task<T> InvokeExportAsync<T>(string moduleName, string exportedFunctionName, params object[] args);
+
+        [Obsolete("Use InvokeAsync instead")]
+        Task<T> Invoke<T>(string moduleName, params object[] args);
+
+        [Obsolete("Use InvokeExportAsync instead")]
+        Task<T> InvokeExport<T>(string moduleName, string exportedFunctionName, params object[] args);
+    }
+}