A background drawn at the artboard's own position could sit 3e-14 pt outside it and
stay behind when the artboard moved, was copied or scaled its art. Art within a
millionth of a point of the artboard's edges now counts as inside it.
The fix and both tests are from #1295 by Luca Lorenz, without its change to art that
only partly overlaps the artboard.
Co-authored-by: Luca Lorenz <lucalorenzetti1993@gmail.com>