SVG <text>: writing-mode & text-orientation

writing-mode: vertical-rl/vertical-lr on an SVG <text> root advances the pen down the column instead of along a line; text-orientation classifies each glyph (mixed, the default) or forces one answer for every glyph (upright/sideways) - CJK reads upright, Latin/digits rotate 90°, the same Unicode Vertical_Orientation classification the HTML pipeline uses. (docs/supported-svg-features.md)

1 — text-orientation: mixed, upright & sideways

2 — vertical-rl vs vertical-lr, and a rotated fill gradient