containments/panel: `spacingAtMinSize` use Math.floor
The `spacingAtMinSize` will be used to calculate the container margins. `Math.floor` is used to get a more consistent scaling when the panel height is changed BUG: 454810
The `spacingAtMinSize` will be used to calculate the container margins. `Math.floor` is used to get a more consistent scaling when the panel height is changed BUG: 454810
mentioned in commit ce9515f4