Added event MessagesReceived for better visibility on receiving side (#1655)

* Added event `MessagesReceived` for better visibility on receiving side

* Fixes/comments from PR

* Final cleanup

bridges/modules/messages/src/inbound_lane.rs

@@ -21,9 +21,8 @@ use crate::Config;
 use bp_messages::{
 	target_chain::{DispatchMessage, DispatchMessageData, MessageDispatch},
 	DeliveredMessages, InboundLaneData, LaneId, MessageKey, MessageNonce, OutboundLaneData,
-	UnrewardedRelayer,
+	ReceivalResult, UnrewardedRelayer,
 };
-use bp_runtime::messages::MessageDispatchResult;
 use codec::{Decode, Encode, EncodeLike, MaxEncodedLen};
 use frame_support::{traits::Get, RuntimeDebug};
 use scale_info::{Type, TypeInfo};
@@ -108,22 +107,6 @@ impl<T: Config<I>, I: 'static> MaxEncodedLen for StoredInboundLaneData<T, I> {
 	}
 }
 
-/// Result of single message receival.
-#[derive(RuntimeDebug, PartialEq, Eq)]
-pub enum ReceivalResult {
-	/// Message has been received and dispatched. Note that we don't care whether dispatch has
-	/// been successful or not - in both case message falls into this category.
-	///
-	/// The message dispatch result is also returned.
-	Dispatched(MessageDispatchResult),
-	/// Message has invalid nonce and lane has rejected to accept this message.
-	InvalidNonce,
-	/// There are too many unrewarded relayer entries at the lane.
-	TooManyUnrewardedRelayers,
-	/// There are too many unconfirmed messages at the lane.
-	TooManyUnconfirmedMessages,
-}
-
 /// Inbound messages lane.
 pub struct InboundLane<S> {
 	storage: S,
@@ -181,12 +164,12 @@ impl<S: InboundLaneStorage> InboundLane<S> {
 	}
 
 	/// Receive new message.
-	pub fn receive_message<P: MessageDispatch<AccountId>, AccountId>(
+	pub fn receive_message<Dispatch: MessageDispatch<AccountId>, AccountId>(
 		&mut self,
 		relayer_at_bridged_chain: &S::Relayer,
 		relayer_at_this_chain: &AccountId,
 		nonce: MessageNonce,
-		message_data: DispatchMessageData<P::DispatchPayload>,
+		message_data: DispatchMessageData<Dispatch::DispatchPayload>,
 	) -> ReceivalResult {
 		let mut data = self.storage.data();
 		let is_correct_message = nonce == data.last_delivered_nonce() + 1;
@@ -206,7 +189,7 @@ impl<S: InboundLaneStorage> InboundLane<S> {
 		}
 
 		// then, dispatch message
-		let dispatch_result = P::dispatch(
+		let dispatch_result = Dispatch::dispatch(
 			relayer_at_this_chain,
 			DispatchMessage {
 				key: MessageKey { lane_id: self.storage.id(), nonce },