Add delegates and VTables for ITaskBarList2.

src/Windows/Avalonia.Win32/ITaskBarList2VTable.cs

@@ -0,0 +1,22 @@
+using System;
+using System.Runtime.InteropServices;
+using static Avalonia.Win32.Interop.UnmanagedMethods;
+
+namespace Avalonia.Win32
+{
+    delegate void MarkFullscreenWindow(IntPtr This, IntPtr hwnd, [MarshalAs(UnmanagedType.Bool)] bool fullscreen);
+    delegate HRESULT HrInit(IntPtr This);
+
+    struct ITaskBarList2VTable
+    {
+        public IntPtr IUnknown1;
+        public IntPtr IUnknown2;
+        public IntPtr IUnknown3;
+        public IntPtr HrInit;
+        public IntPtr AddTab;
+        public IntPtr DeleteTab;
+        public IntPtr ActivateTab;
+        public IntPtr SetActiveAlt;
+        public IntPtr MarkFullscreenWindow;
+    }
+}