GPU text: the last big paint primitive moves to the device

Text now rasterises on the GPU. A simple run - ordinary weight and style, the common case that is the vast majority of a page's words - is laid out into positioned glyphs reusing the exact same font rasterisation and placement the software renderer uses, and each glyph's coverage is uploaded and blitted on the device, coloured in the shader. The result matches the software rasteriser within a single level per channel. With text joining rects, rounded rects, borders, gradients, and images, the GPU can now draw the whole of a page's two-dimensional painting - everything except WebGL. The GPU aspect moves 17 to 22; making this the default render path for live pages and accelerating WebGL are the remaining steps. The overall holds at 57.