This creates a new Renderer type that offers fairly simple render_to_texture and render_to_surface methods, the latter of which handles the final blit internally. Also adds a util module with some helpers for device and surface creation.
There is a new winit example in piet-wgsl/examples/winit that shows how to make use of it all. This should be fairly trivial to adapt to glazier/xilem.
* add writeable image support to engine
* add external resources to engine
* update fine to output to a texture
* copy over original piet-gpu test scenes
* put it all in a pretty (resizable!) window