font_props wrote `bold` for any style whose name contained bold, black
or heavy and nothing for the others unless fonts were embedded, so
Semibold came back Bold and Light or Medium came back Regular. It now
writes the style's numeric weight (font_descriptor, from style_weight)
for every writer: 600 for Semibold, 300 for Light, 900 for Black, `bold`
for 700 and nothing for 400. The SVG import already reads these numbers
back to the matching face.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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