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.rs

@@ -0,0 +1,10 @@
+use crate::messages::prelude::*;
+
+#[impl_message(Message, Defer)]
+#[derive(PartialEq, Clone, Debug, serde::Serialize, serde::Deserialize)]
+pub enum DeferMessage {
+	TriggerGraphRun(u64),
+	AfterGraphRun { messages: Vec<Message> },
+	TriggerNavigationReady,
+	AfterNavigationReady { messages: Vec<Message> },
+}