pad of a given number.
Also improves other DRC logic to tighten up the net-tie rules now that
we know which pads are allowed to short with which other pads.
Also removes the "Overlapping pads" DRC violation now that we know
whether or not overlapping pads in a net-tie footprint constitute a
short.
Fixes https://gitlab.com/kicad/code/kicad/issues/12506