Shaders: add BufferStruct to support bool and enums (#3109)

* node-macro: modernize `node` macro

* node-macro: add `CrateIdent` struct containing resolved crate paths

* shaders: add trait `BufferStruct` and derive macro

* shaders: `gamma_correction` and `channel_mixer` gpu nodes

* shaders: `selective_color` gpu node

* shaders: `brightness_contrast_classic` gpu node

* shaders: append GPU to display name

* node-macro: fixup doc links

* shaders: consistently append " GPU" to all shader node names

node-graph/node-macro/src/crate_ident.rs

@@ -0,0 +1,46 @@
+use proc_macro_crate::{FoundCrate, crate_name};
+use proc_macro2::{Span, TokenStream};
+use quote::{format_ident, quote};
+
+pub struct CrateIdent {
+	gcore: syn::Result<TokenStream>,
+	gcore_shaders: syn::Result<TokenStream>,
+	wgpu_executor: syn::Result<TokenStream>,
+}
+
+impl CrateIdent {
+	pub fn gcore(&self) -> syn::Result<&TokenStream> {
+		self.gcore.as_ref().map_err(Clone::clone)
+	}
+
+	pub fn gcore_shaders(&self) -> syn::Result<&TokenStream> {
+		self.gcore_shaders.as_ref().map_err(Clone::clone)
+	}
+
+	pub fn wgpu_executor(&self) -> syn::Result<&TokenStream> {
+		self.wgpu_executor.as_ref().map_err(Clone::clone)
+	}
+}
+
+impl Default for CrateIdent {
+	fn default() -> Self {
+		let find_crate = |orig_name| match crate_name(orig_name) {
+			Ok(FoundCrate::Itself) => Ok(quote!(crate)),
+			Ok(FoundCrate::Name(name)) => {
+				let name = format_ident!("{}", name);
+				Ok(quote!(::#name))
+			}
+			Err(e) => Err(syn::Error::new(Span::call_site(), &format!("Could not find dependency on `{orig_name}`:\n{e}"))),
+		};
+
+		let gcore = find_crate("graphene-core");
+		let gcore_shaders = find_crate("graphene-core-shaders").or_else(|eshaders| {
+			gcore
+				.as_ref()
+				.map(Clone::clone)
+				.map_err(|ecore| syn::Error::new(Span::call_site(), &format!("{ecore}\n\nFallback: {eshaders}")))
+		});
+		let wgpu_executor = find_crate("wgpu-executor");
+		Self { gcore, gcore_shaders, wgpu_executor }
+	}
+}