Restructure the entire editor codebase to consistently match the message hierarchy

Closes #744

editor/src/messages/workspace/mod.rs

@@ -0,0 +1,7 @@
+mod workspace_message;
+mod workspace_message_handler;
+
+#[doc(inline)]
+pub use workspace_message::{WorkspaceMessage, WorkspaceMessageDiscriminant};
+#[doc(inline)]
+pub use workspace_message_handler::WorkspaceMessageHandler;

editor/src/messages/workspace/workspace_message.rs

@@ -0,0 +1,11 @@
+use crate::messages::prelude::*;
+
+use serde::{Deserialize, Serialize};
+
+#[remain::sorted]
+#[impl_message(Message, Workspace)]
+#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
+pub enum WorkspaceMessage {
+	// Messages
+	NodeGraphToggleVisibility,
+}

editor/src/messages/workspace/workspace_message_handler.rs

@@ -0,0 +1,28 @@
+use crate::messages::prelude::*;
+
+#[derive(Debug, Clone, Default)]
+pub struct WorkspaceMessageHandler {
+	node_graph_visible: bool,
+}
+
+impl MessageHandler<WorkspaceMessage, &InputPreprocessorMessageHandler> for WorkspaceMessageHandler {
+	#[remain::check]
+	fn process_message(&mut self, message: WorkspaceMessage, _ipp: &InputPreprocessorMessageHandler, responses: &mut VecDeque<Message>) {
+		use WorkspaceMessage::*;
+
+		#[remain::sorted]
+		match message {
+			// Messages
+			NodeGraphToggleVisibility => {
+				self.node_graph_visible = !self.node_graph_visible;
+				responses.push_back(FrontendMessage::UpdateNodeGraphVisibility { visible: self.node_graph_visible }.into());
+			}
+		}
+	}
+
+	fn actions(&self) -> ActionList {
+		actions!(WorkspaceMessageDiscriminant;
+			NodeGraphToggleVisibility,
+		)
+	}
+}