usvg takes a `transform` CSS property as a presentation attribute that
overrides the element's own, but reads its value as SVG: CSS units
(`translate(100px, 0)`, `rotate(45deg)`) don't parse, and the object
was left with no transform at all. Before usvg runs, transform
declarations in `style` attributes and `<style>` rules are now written
in SVG syntax (lengths in px, angles in deg/rad/grad/turn, translateX/Y,
scaleX/Y and skew as SVG's functions); values that can't be are left.
The text pass's own cascade now expands the `font` shorthand into its
longhands, as usvg does for the rest of the drawing, so text styled
with `font: italic bold 30px …` keeps its size, weight and style.
Refs #1557
2c01a42b35