Revert "Panel: don't double count floatingPadding"

This reverts commit 8ead01b3.

Sorry, I didn't manage to review the original MR !2222 (merged) in an appropriate amount of time. The commit has to be reverted because the distance is meant to avoid the window snapping to the floating panel window, which extends beyond the panel itself. By decreasing the de-floating margin value, we are much more prone to buggy snapping when dragging a window near a floating panel. We instead need to disable window snapping for panels.