Returns a vector with elements equal to the
edge lengths of the rectangle. The returned vector is not
used to represent the rectangle internally, so changing its
values will not affect the state of the rectangle.
This method should be defined by the subclass to calculate the vertices
in accordance with the internal representation of the polytope. If the
internal representation is kept by the vertices themselves, then this
method need do nothing; if this method applies another internal
representation to the vertices (for example, it might represent a square
by keeping the edge length), it should then invoke
applyTranslationRotation() before returning. Subclass methods allowing
mutation of the internal representation should invoke updateVertices to
ensure the vertices reflect the internal state. Vertices may be
changed directly, but these changes will overridden by updateVertices if
it is called afterwards.