Adds kurbo as an optional dependency and implements conversions to/from the common types.
This also removes the direct pinot dependency and changes moscato (temporarily) to a git based dep to allow iteration on the underlying glyph loading code without PR churn here.
* Change pgpu-render header file generator to add a comment noting that the file is auto-generated
* Remove bin target and associated dependencies from piet-scene crate
* Remove FP constructors from the Color type
* Better codegen and rounding in Color::to_premul_u32()
* Add kurbo attribution for piet_scene::geometry module
This commit implements actual rendering for the new piet-scene crate.
In particular, it adds a new EncodedSceneRef type in piet_gpu::encoder to store references to the raw stream data. This is used as a proxy for both PietGpuRenderContext and piet_scene::scene::Scene to feed data into the renderer.
Much of this is still hacky for expedience and because the intention is to be a transitional state that maintains both interfaces until we can move to the new scene API and add a wrapper for the traditional piet API.
The general structure and relationships between these crates need further discussion.
