Add OS-specific interop

Source/_Demos/LoadByOS/CrossPlatformClientExe/OSConfigBase.cs

@@ -0,0 +1,29 @@
+using System;
+
+namespace CrossPlatformClientExe
+{
+    public abstract class OSConfigBase
+    {
+        public abstract Type InteropFunctionsType { get; }
+        public virtual Type[] ReferencedTypes { get; } = new Type[0];
+
+        public void Run()
+        {
+            //Each of these types belongs to a different windows-only assembly that's needed by
+            //the WinInterop methods. By referencing these types in main we force the runtime to
+            //load their assemblies before execution reaches inside main. This allows the calling
+            //process to find these assemblies in its module list.
+            _ = ReferencedTypes;
+            _ = InteropFunctionsType;
+
+            //Wait for the calling process to be ready to read the WriteLine()
+            Console.ReadLine();
+
+            // Signal the calling process that execution has reached inside main, and that all referenced assemblies have been loaded.
+            Console.WriteLine();
+
+            // Wait for the calling process to finish reading the process module list, then exit.
+            Console.ReadLine();
+        }
+    }
+}