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/mock.rs

@@ -20,6 +20,7 @@
 
 use crate::{peer_store::PeerStoreProvider, protocol_controller::ProtocolHandle, ReputationChange};
 use libp2p::PeerId;
+use sc_network_common::role::ObservedRole;
 use std::collections::HashSet;
 
 /// No-op `PeerStore`.
@@ -49,6 +50,14 @@ impl PeerStoreProvider for MockPeerStore {
 		0
 	}
 
+	fn peer_role(&self, _peer_id: &PeerId) -> Option<ObservedRole> {
+		None
+	}
+
+	fn set_peer_role(&mut self, _peer_id: &PeerId, _role: ObservedRole) {
+		unimplemented!();
+	}
+
 	fn outgoing_candidates(&self, _count: usize, _ignored: HashSet<&PeerId>) -> Vec<PeerId> {
 		unimplemented!()
 	}