The second half of #966. With Proportional Metrics on, a vertical segment is
also shaped top to bottom, with and without `vpal`: the difference gives
each glyph's change of advance down the column and its x and y placement.
An upright glyph (not tate-chu-yoko) in a font with vertical metrics takes
them on top of its cell, so it moves with its shorter cell; a font without
vertical metrics keeps `upright_cell`'s cell, and with the switch off
nothing is shaped twice and the column is as before.
As in horizontal type, Line-end Punctuation Half Width takes nothing more
off the punctuation `vpal` re-spaced and trims the punctuation it leaves
full height as before. Docs: mcp.md, and Proportional Metrics leaves the
missing lists in gaps.md, type-parity.md and target-app-parity.md.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
2c8b8b0cc1