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

editor/src/messages/broadcast/broadcast_event.rs

@@ -1,8 +1,6 @@
 use crate::messages::prelude::*;
 
-use serde::{Deserialize, Serialize};
-
-#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize, Hash)]
+#[derive(PartialEq, Eq, Clone, Debug, serde::Serialize, serde::Deserialize, Hash)]
 #[impl_message(Message, BroadcastMessage, TriggerEvent)]
 pub enum BroadcastEvent {
 	AnimationFrame,

editor/src/messages/broadcast/broadcast_message.rs

@@ -1,9 +1,7 @@
 use crate::messages::prelude::*;
 
-use serde::{Deserialize, Serialize};
-
 #[impl_message(Message, Broadcast)]
-#[derive(PartialEq, Clone, Debug, Serialize, Deserialize)]
+#[derive(PartialEq, Clone, Debug, serde::Serialize, serde::Deserialize)]
 pub enum BroadcastMessage {
 	// Sub-messages
 	#[child]