Gets the transform from the shading's target space, where its coordinates and BBox are given, to the page's default user
space: the CTM at sh, or pattern space (the pattern matrix followed by the space of the stream that selected the
pattern) for a shading pattern. It does not depend on the transform SetTransform(in Matrix) set.
public Matrix Matrix { get; }
ISO 32000-2 §8.7.4.2 (sh: the current user space), §8.7.2 and §8.7.4.1 (pattern space).