Gets the 12-byte Panose classification of a CIDFont's glyphs, from the Panose entry of its Style dictionary: the
font family class and subclass of the "OS/2" table, then the ten PANOSE bytes; null when absent or not 12 bytes.
public ReadOnlyMemory<byte>? Panose { get; }
ISO 32000-2 §9.8.3.1, Table 122 (Style), and §9.8.3.2.