Shaders: runtime and shader node codegen (#2985)

* shader-rt: initial

* shader-rt: fix recursion when generating shader node

* shader-rt: replace gpu node's args and ret types with `Raster<GPU>`

* shader-rt: properly cfg out the gpu node

* shader-rt: fix `impl Context` in the wrong places

* shader-rt: disable gpu blend node, needs two images

* shader-rt: connect shader runtime

* shader-rt: pass WgpuExecutor by reference

* shader-rt: correct bindings with derpy arg buffer

* shader-rt: manual pipeline layout, fixing errors when bindings got DCE'd

* shader-rt: correct RT format, working invert gpu node

* shader-rt: cleanup codegen with common sym struct

* shader-rt: correct arg buffer handling

* shader-nodes feature: put shader nodes behind feature gate

* shader-nodes feature: rename any `gpu_node` to `shader-node`

* shaders-rt: fix wgpu label name

* shaders-rt: explain fullscreen_vertex coordinates with a drawing

node-graph/graster-nodes/src/lib.rs

@@ -4,6 +4,11 @@ pub mod adjust;
 pub mod adjustments;
 pub mod blending_nodes;
 pub mod cubic_spline;
+pub mod fullscreen_vertex;
+
+/// required by shader macro
+#[cfg(feature = "shader-nodes")]
+pub use graphene_raster_nodes_shaders::WGSL_SHADER;
 
 #[cfg(feature = "std")]
 pub mod curve;