Upload structural shape attrs (base, children, blur, shadows,
flex, layout-item) via multi-shape `_set_shapes_batch` FFI in
chunks of 512, then apply host attrs with use-shape selection.
* ✨ Add text and @font-face to WASM SVG export
Emit selectable <text> elements and inject @font-face rules that
reference the font URLs registered at load time. Text fill bypasses
save_layer wrappers that SkSVGDevice drops. Text strokes are deferred
to a follow-up PR.
* 🐛 Strip trailing commas from Skia SVG text positions
Skia's SVG backend appends a trailing comma to per-glyph x/y lists.
Firefox rejects the malformed attribute and drops glyph positioning,
making exported text vanish or mis-render.
