Window Class Refactor: Invention List Drag (#17415)

* Start working on drag

* Finish moving invention drag into window class

* Refactor drag item into a window variable

* Remove rct2 comment

src/openrct2/interface/Window_internal.cpp

@@ -2,6 +2,7 @@
 
 #include "../entity/EntityList.h"
 #include "../entity/EntityRegistry.h"
+#include "Cursors.h"
 #include "Viewport.h"
 
 void rct_window::SetLocation(const CoordsXYZ& coords)
@@ -35,3 +36,8 @@ void rct_window::RemoveViewport()
     viewport_remove(viewport);
     viewport = nullptr;
 }
+
+CursorID rct_window::OnCursor(rct_widgetindex, const ScreenCoordsXY&, CursorID)
+{
+    return CursorID::Arrow;
+}