Restructure GPU execution to model GPU pipelines in the node graph (#1088)

* Start implementing GpuExecutor for wgpu

* Implement read_output_buffer function

* Implement extraction node in the compiler

* Generate type annotations during shader compilation

* Start adding node wrapprs for graph execution api

* Wrap more of the api in nodes

* Restructure Pipeline to accept arbitrary shader inputs

* Adapt nodes to new trait definitions

* Start implementing gpu-compiler trait

* Adapt shader generation

* Hardstuck on pointer casts

* Pass nodes as references in gpu code to avoid zsts

* Update gcore to compile on the gpu

* Fix color doc tests

* Impl Node for node refs

node-graph/gcore/src/gpu.rs

@@ -1,4 +1,7 @@
+use crate::{raster::Sample, Color};
+
 use bytemuck::{Pod, Zeroable};
+use spirv_std::image::{Image2d, SampledImage};
 
 #[repr(C)]
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Pod, Zeroable)]
@@ -6,3 +9,12 @@ pub struct PushConstants {
 	pub n: u32,
 	pub node: u32,
 }
+
+impl Sample for SampledImage<Image2d> {
+	type Pixel = Color;
+
+	fn sample(&self, pos: glam::DVec2) -> Option<Self::Pixel> {
+		let color = self.sample(pos);
+		Color::from_rgbaf32(color.x, color.y, color.z, color.w)
+	}
+}