Gets the vertical metrics of a CID's glyph: its W2 entry, else DW2 with v.x half the glyph's width.
public CidVerticalMetrics GetVerticalMetrics(int cid)
The CID.
ISO 32000-2 §9.7.4.3; §9.9.1: vertical metrics come only from these entries, never from the program's "vhea"/"vmtx".