Add handler for deferred execution of messages (#2951)

* Add Handler for defered execution of messages

* Cleanup

* Track graph execution id to associate messages with their corresponding execution id

* Rename ViewportReady -> NavigationReady

* Defer layer deselection

editor/src/messages/defer/defer_message_handler.rs

@@ -0,0 +1,36 @@
+use crate::messages::prelude::*;
+
+#[derive(Debug, Default, ExtractField)]
+pub struct DeferMessageHandler {
+	after_graph_run: Vec<(u64, Message)>,
+	after_viewport_resize: Vec<Message>,
+	current_graph_submission_id: u64,
+}
+
+#[message_handler_data]
+impl MessageHandler<DeferMessage, ()> for DeferMessageHandler {
+	fn process_message(&mut self, message: DeferMessage, responses: &mut VecDeque<Message>, _: ()) {
+		match message {
+			DeferMessage::AfterGraphRun { mut messages } => {
+				self.after_graph_run.extend(messages.drain(..).map(|m| (self.current_graph_submission_id, m)));
+			}
+			DeferMessage::AfterNavigationReady { messages } => {
+				self.after_viewport_resize.extend_from_slice(&messages);
+			}
+			DeferMessage::TriggerGraphRun(execution_id) => {
+				self.current_graph_submission_id = execution_id;
+				for message in self.after_graph_run.extract_if(.., |x| x.0 < self.current_graph_submission_id) {
+					responses.push_front(message.1);
+				}
+			}
+			DeferMessage::TriggerNavigationReady => {
+				for message in self.after_viewport_resize.drain(..) {
+					responses.push_front(message);
+				}
+			}
+		}
+	}
+
+	advertise_actions!(DeferMessageDiscriminant;
+	);
+}