useSortable with variable size items and without a drag overlay

[ceddlyburge]

Hi There, and thanks for the great library!

We created a vertical list recently, with useSortable, and couldn't get the dragging / collision detection to work with our variable height items, without also using an overlay. The overlay was difficult to achieve for us, for reasons I won't go in to.

Anyway, we created a new collision detection strategy that allows it to work as you would expect, so if you want this I can open up a pull request. If not feel free to close the issue.

Thanks, Cedd

[clauderic]

Feel free to open a pull request and we can discuss there 👍

[ceddlyburge]

#805 :)