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/blending_nodes.rs

@@ -132,7 +132,7 @@ pub fn apply_blend_mode(foreground: Color, background: Color, blend_mode: BlendM
 	}
 }
 
-#[node_macro::node(category("Raster"), shader_node(PerPixelAdjust))]
+#[node_macro::node(category("Raster"), cfg(feature = "std"))]
 fn blend<T: Blend<Color> + Send>(
 	_: impl Ctx,
 	#[implementations(