Better polygon rendering in LibreOffice's Gtk3 Support

Above is how LibreOffice's "svp" backend rendered rotated text outlines in chart where the text is represented by polygon paths. Because the gtk3 backend is based on that svp backend that's what you got with the gtk3 support enabled.

After today's work above is how the svp backend now renders those paths when rendering to a cairo-compatible surface such as the gtk3 support provides.

If we mandate that "svp" only operates on cairo compatible surfaces, then we can get this niceness into android and online too, and can ditch our non-cairo text rendering code paths.