Gets the glyph's box in page space: from its origin to its horizontal displacement w0 along the baseline, and from the font's descent to its ascent across it, mapped by the text rendering matrix and the CTM.
public Quad Quad { get; }
ISO 32000-2 §9.4.4 (T_rm × CTM), §9.2.4 (w0) and §9.8.1 (Table 120, Ascent and Descent; FontBBox
when they are missing; for a Type 3 font the FontBBox through the FontMatrix, §9.6.4). A font with neither uses
0.8 above and 0.2 below the baseline, as other processors do. The box is the font's, not the glyph's outline.