porting shell from nuget to local

src/Shared/Microsoft.Windows.Shell/Standard/GWL.cs

@@ -0,0 +1,15 @@
+using System;
+
+namespace Standard
+{
+	internal enum GWL
+	{
+		WNDPROC = -4,
+		HINSTANCE = -6,
+		HWNDPARENT = -8,
+		STYLE = -16,
+		EXSTYLE = -20,
+		USERDATA = -21,
+		ID = -12
+	}
+}