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/message.rs

@@ -1,5 +1,4 @@
 use crate::messages::prelude::*;
-use graphene_std::renderer::RenderMetadata;
 use graphite_proc_macros::*;
 
 #[impl_message]
@@ -15,6 +14,8 @@ pub enum Message {
 	#[child]
 	Debug(DebugMessage),
 	#[child]
+	Defer(DeferMessage),
+	#[child]
 	Dialog(DialogMessage),
 	#[child]
 	Frontend(FrontendMessage),
@@ -40,10 +41,6 @@ pub enum Message {
 	Batched {
 		messages: Box<[Message]>,
 	},
-	StartBuffer,
-	EndBuffer {
-		render_metadata: RenderMetadata,
-	},
 }
 
 /// Provides an impl of `specta::Type` for `MessageDiscriminant`, the struct created by `impl_message`.