Reliable script to handle selection/drag-and-drop in a list field?

[Geoff Canyon]

Does anyone have code to share that allows discontiguous selection and drag
and drop within a list field? i.e. if I have a list field with:

1
2
3
4
5

I can click 3 to select it, shift-click 5 to select 3 to 5, command-click 4
so that 3 and 5 are selected, and then click and drag 3 (with 5 along for
the ride) above 2 and end up with:

1
3
5
2
4