Convert drag/drop code to use shared implementation

The shared code is available, but WPF has not been converted to use it.

https://github.com/dotnet/winforms/blob/main/src/System.Private.Windows.Core/src/System/Private/Windows/Ole/DragDropHelper.cs

This has not been investigated yet. Code paths would need compared between WinForms and WPF to ensure the shared code satisfies WPF needs. @JeremyKuhne and @Tanya-Solyanik can be consulted.