Fix dragging onto complex items

[skeemer]

Fix dragging onto complex items where the space is completely covered by child elements

[hesamurai]

Thanks @skeemer for contributing to this library.
I need to see the usage of this code in action. Don't you mind adding a sample for it please (inside https://github.com/hesamurai/nested-sort/tree/main/dev)?

[skeemer]

I've added an example. If you run that on the main branch js, you'll notice that entering other items doesn't always get picked up.