GPU filled polygons: vector fills join the device path

Filled polygons - the shapes behind SVG polygons and CSS clip-path fills - now rasterise on the GPU. Each pixel runs the same four-by-four supersampled even-odd point-in-polygon test the software renderer uses, so interiors are bit-exact and only the anti-aliased edge differs by a single coverage level. With this, vector fills join the solid, gradient, image, text, shadow, clip, transform, and filter primitives already on the device - the software renderer no longer holds any 2D fill class to itself. The GPU aspect moves 46 to 47. The remaining work toward full acceleration is unchanged: making the GPU renderer the default live path, WebGL, and hardware video decode. The overall holds at 57.