Draft: taskfilterproxymodel: shrink regionGeometry by 1
Shrink by 1 to avoid false positives caused by rounding errors. Since QWindow reports its geometry in ints, using QRectF doesn't help. This supports dodge-windows panels between two screens, which is only supported on wayland, so we don't need to worry about X11.
Only needed if we merge kwin!5166 (merged)