Prep gcore splitup: move various symbols into their own modules (#2746)

* move `trait AsU32` from `gcore::vector::misc` to `gcore`

* move blending and gradient to their own modules

* fix unused warnings

* move `Quad`, `Rect` and `BBox` to `gcore::math`

* extract `ReferencePoint` and transform nodes from `transform`

* move color-related code to `mod color`

* fix unused warning in test code

* move blending-related nodes and code to `mod blending_nodes`

* move ClickTarget code to `mod vector::click_target`

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

@@ -168,7 +168,7 @@ fn derive_enum(enum_attributes: &[Attribute], name: Ident, input: syn::DataEnum)
 		WidgetHint::Dropdown => quote! { Dropdown },
 	};
 	Ok(quote! {
-		impl #crate_name::vector::misc::AsU32 for #name {
+		impl #crate_name::AsU32 for #name {
 			fn as_u32(&self) -> u32 {
 				*self as u32
 			}