Gets what the glyph's description declares when Font is a Type 3 font: whether it began with d0 (shape
and colour) or d1 (shape only, painted in the text's colour), the width it gives and the d1 bounding box, in glyph
space (FontMatrix maps it to text space). Kind None for other fonts and
for a code with no description.
public Type3GlyphMetrics Type3Metrics { get; }
ISO 32000-2 §9.6.4, Table 111. Read from the description's first operator without running it, so it is the same when the glyph
is shown, when its description is entered (BeginType3Glyph(in GlyphEvent, ContentContext)) and after it ran, and for a glyph
whose description is not run (text rendering modes 3 and 7); a processor can decide how to cache the glyph before entering it.
A description that begins with neither operator is Undeclared and runs as d0. Allocates
nothing once the description was read.