Relay basic single-bit message dispatch results back to the source chain (#935)

* relay dispatch result flags back to the source chain

* OnMessagesDelivered callback

* add lane id to OnDeliveredMessages callback

* fix benchmarks && upate weights

* clippy

* clippy

* clipy another try

* OnMessagesDelivered -> OnDeliveryConfirmed

* Update primitives/messages/src/source_chain.rs

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

bridges/primitives/messages/src/source_chain.rs

@@ -16,7 +16,7 @@
 
 //! Primitives of messages module, that are used on the source chain.
 
-use crate::{InboundLaneData, LaneId, MessageNonce, OutboundLaneData};
+use crate::{DeliveredMessages, InboundLaneData, LaneId, MessageNonce, OutboundLaneData};
 
 use bp_runtime::Size;
 use frame_support::{Parameter, RuntimeDebug};
@@ -135,6 +135,15 @@ pub trait MessageDeliveryAndDispatchPayment<AccountId, Balance> {
 	}
 }
 
+/// Handler for messages delivery confirmation.
+#[impl_trait_for_tuples::impl_for_tuples(30)]
+pub trait OnDeliveryConfirmed {
+	/// Called when we receive confirmation that our messages have been delivered to the
+	/// target chain. The confirmation also has single bit dispatch result for every
+	/// confirmed message (see `DeliveredMessages` for details).
+	fn on_messages_delivered(_lane: &LaneId, _messages: &DeliveredMessages) {}
+}
+
 /// Structure that may be used in place of `TargetHeaderChain`, `LaneMessageVerifier` and
 /// `MessageDeliveryAndDispatchPayment` on chains, where outbound messages are forbidden.
 pub struct ForbidOutboundMessages;