issue with drag drop in scrollable area

if target element is in scroll, dragged element is not getting dropped at correct position.

Start by reproducing the drag-and-drop behavior when the target element is inside a scrollable area, recording the expected and actual drop positions. Trace the relevant drag and drop event handling in the library; done means the dragged element lands at the correct position in the scrollable target.

Written by the indexing model from the issue text.