Implement editor level future message handler (#4182)

* Implement proper editor level async message handler

* Take application_io and wake callback as Editor::new arguments

* Rename AsyncMessage -> FutureMessage

* add DesktopWrapperMessage::Wake

---------

Co-authored-by: Timon <me@timon.zip>

editor/src/messages/future/future_message.rs

@@ -0,0 +1,16 @@
+use crate::messages::future::MessageFuture;
+use crate::messages::prelude::*;
+
+#[impl_message(Message, Future)]
+#[derive(derivative::Derivative, Clone, serde::Serialize, serde::Deserialize)]
+#[derivative(Debug, PartialEq)]
+pub enum FutureMessage {
+	/// Spawn `future`; its resolved [`Message`] re-enters the dispatcher on the next tick.
+	Await {
+		#[serde(skip, default)]
+		#[derivative(Debug = "ignore", PartialEq = "ignore")]
+		future: MessageFuture,
+	},
+	/// Sent by a wake callback to nudge an idle event loop into a dispatch tick.
+	Wake,
+}