Show a cursor when dragging and dropping files into a playlist

[simeonrobinson]

When dragging and dropping, the files are put at the end of the playlist and there's no indicator showing where they will be dropped, like when dragging files around within a playlist.

[Taiko2k]

This is currently related to a limitation of the SDL2 library. Once Tauon is ported to the future major release of SDL3, this bug will likely become fixable. But for now it isn't easily fixable.