Rework the event system of sc-network (#1370)

This commit introduces a new concept called `NotificationService` which
allows Polkadot protocols to communicate with the underlying
notification protocol implementation directly, without routing events
through `NetworkWorker`. This implies that each protocol has its own
service which it uses to communicate with remote peers and that each
`NotificationService` is unique with respect to the underlying
notification protocol, meaning `NotificationService` for the transaction
protocol can only be used to send and receive transaction-related
notifications.

The `NotificationService` concept introduces two additional benefits:
  * allow protocols to start using custom handshakes
  * allow protocols to accept/reject inbound peers

Previously the validation of inbound connections was solely the
responsibility of `ProtocolController`. This caused issues with light
peers and `SyncingEngine` as `ProtocolController` would accept more
peers than `SyncingEngine` could accept which caused peers to have
differing views of their own states. `SyncingEngine` would reject excess
peers but these rejections were not properly communicated to those peers
causing them to assume that they were accepted.

With `NotificationService`, the local handshake is not sent to remote
peer if peer is rejected which allows it to detect that it was rejected.

This commit also deprecates the use of `NetworkEventStream` for all
notification-related events and going forward only DHT events are
provided through `NetworkEventStream`. If protocols wish to follow each
other's events, they must introduce additional abtractions, as is done
for GRANDPA and transactions protocols by following the syncing protocol
through `SyncEventStream`.

Fixes https://github.com/paritytech/polkadot-sdk/issues/512
Fixes https://github.com/paritytech/polkadot-sdk/issues/514
Fixes https://github.com/paritytech/polkadot-sdk/issues/515
Fixes https://github.com/paritytech/polkadot-sdk/issues/554
Fixes https://github.com/paritytech/polkadot-sdk/issues/556

---
These changes are transferred from
https://github.com/paritytech/substrate/pull/14197 but there are no
functional changes compared to that PR

---------

Co-authored-by: Dmitry Markin <dmitry@markin.tech>
Co-authored-by: Alexandru Vasile <60601340+lexnv@users.noreply.github.com>

substrate/client/network/src/peer_store.rs

@@ -23,7 +23,7 @@ use libp2p::PeerId;
 use log::trace;
 use parking_lot::Mutex;
 use partial_sort::PartialSort;
-use sc_network_common::types::ReputationChange;
+use sc_network_common::{role::ObservedRole, types::ReputationChange};
 use std::{
 	cmp::{Ord, Ordering, PartialOrd},
 	collections::{hash_map::Entry, HashMap, HashSet},
@@ -66,9 +66,15 @@ pub trait PeerStoreProvider: Debug + Send {
 	/// Adjust peer reputation.
 	fn report_peer(&mut self, peer_id: PeerId, change: ReputationChange);
 
+	/// Set peer role.
+	fn set_peer_role(&mut self, peer_id: &PeerId, role: ObservedRole);
+
 	/// Get peer reputation.
 	fn peer_reputation(&self, peer_id: &PeerId) -> i32;
 
+	/// Get peer role, if available.
+	fn peer_role(&self, peer_id: &PeerId) -> Option<ObservedRole>;
+
 	/// Get candidates with highest reputations for initiating outgoing connections.
 	fn outgoing_candidates(&self, count: usize, ignored: HashSet<&PeerId>) -> Vec<PeerId>;
 }
@@ -96,10 +102,18 @@ impl PeerStoreProvider for PeerStoreHandle {
 		self.inner.lock().report_peer(peer_id, change)
 	}
 
+	fn set_peer_role(&mut self, peer_id: &PeerId, role: ObservedRole) {
+		self.inner.lock().set_peer_role(peer_id, role)
+	}
+
 	fn peer_reputation(&self, peer_id: &PeerId) -> i32 {
 		self.inner.lock().peer_reputation(peer_id)
 	}
 
+	fn peer_role(&self, peer_id: &PeerId) -> Option<ObservedRole> {
+		self.inner.lock().peer_role(peer_id)
+	}
+
 	fn outgoing_candidates(&self, count: usize, ignored: HashSet<&PeerId>) -> Vec<PeerId> {
 		self.inner.lock().outgoing_candidates(count, ignored)
 	}
@@ -122,13 +136,19 @@ impl PeerStoreHandle {
 
 #[derive(Debug, Clone, Copy)]
 struct PeerInfo {
+	/// Reputation of the peer.
 	reputation: i32,
+
+	/// Instant when the peer was last updated.
 	last_updated: Instant,
+
+	/// Role of the peer, if known.
+	role: Option<ObservedRole>,
 }
 
 impl Default for PeerInfo {
 	fn default() -> Self {
-		Self { reputation: 0, last_updated: Instant::now() }
+		Self { reputation: 0, last_updated: Instant::now(), role: None }
 	}
 }
 
@@ -242,10 +262,27 @@ impl PeerStoreInner {
 		}
 	}
 
+	fn set_peer_role(&mut self, peer_id: &PeerId, role: ObservedRole) {
+		log::trace!(target: LOG_TARGET, "Set {peer_id} role to {role:?}");
+
+		match self.peers.entry(*peer_id) {
+			Entry::Occupied(mut entry) => {
+				entry.get_mut().role = Some(role);
+			},
+			Entry::Vacant(entry) => {
+				entry.insert(PeerInfo { role: Some(role), ..Default::default() });
+			},
+		}
+	}
+
 	fn peer_reputation(&self, peer_id: &PeerId) -> i32 {
 		self.peers.get(peer_id).map_or(0, |info| info.reputation)
 	}
 
+	fn peer_role(&self, peer_id: &PeerId) -> Option<ObservedRole> {
+		self.peers.get(peer_id).map_or(None, |info| info.role)
+	}
+
 	fn outgoing_candidates(&self, count: usize, ignored: HashSet<&PeerId>) -> Vec<PeerId> {
 		let mut candidates = self
 			.peers