Gets the matrix from text space to user space for this glyph: [T_fs·T_h 0 0 T_fs 0 T_rise] × T_m, with the glyph's
origin at text space's origin (for vertical writing the position vector is already subtracted, §9.7.4.3).
public Matrix TextMatrix { get; }
ISO 32000-2 §9.4.4. The CTM is the transform set before the run (SetTransform(in Matrix)).