Make Painted Runway signs editable like parking spot numbers

When using the PaintedLine object type HOLD_SHORT_FORWARD_MARKED or the
backward version, it would be great if we could edit the position of the
marking on the taxiway in the same way that we can edit parking numbers that
are painted on the ground. I’ve run in to some situations where the signs
don’t show at all when the marking has more than 2 nodes, and when they don’t
properly split a painted enhance