Code cleanup and refactoring to enhance consistency (#1695)

- Move message handler payload data into structs
- Organize the file structure used by `editor/src/messages/portfolio/document` `/node_graph` and `/graph_operation`
- Make derive attributes use `serde::Serialize, serde::Deserialize` consistently instead of `use serde::{Deserialize, Serialize};` imports
- Various other code cleanup and refactoring

node-graph/gcore/src/structural.rs

@@ -175,9 +175,8 @@ impl<'input, S0: 'input, O: 'static> ApplyNode<O, S0> {
 
 #[cfg(test)]
 mod test {
-	use crate::{ops::IdentityNode, value::ValueNode};
-
 	use super::*;
+	use crate::{ops::IdentityNode, value::ValueNode};
 
 	#[test]
 	fn compose() {