This allows common operations like merging a pin courtyard
into the body courtyard in the fooprint editor, taking a
"bite" out of a polygon and so on,
For now, this only supports polygons made of straight lines.
There are some wierd cases when the operations result in nothing
(e.g. wen a big polygon is substracted from a smaller one that
it contains entirely). I have tried to do something senisble in
these cases, but there may be more optimal ways to handle it.
Relates-To: https://gitlab.com/kicad/code/kicad/-/issues/13025
John Beard