Extract syncing protocol from sc-network (#12828)

* Move import queue out of `sc-network`

Add supplementary asynchronous API for the import queue which means
it can be run as an independent task and communicated with through
the `ImportQueueService`.

This commit removes removes block and justification imports from
`sc-network` and provides `ChainSync` with a handle to import queue so
it can import blocks and justifications. Polling of the import queue is
moved complete out of `sc-network` and `sc_consensus::Link` is
implemented for `ChainSyncInterfaceHandled` so the import queue
can still influence the syncing process.

* Move stuff to SyncingEngine

* Move `ChainSync` instanation to `SyncingEngine`

Some of the tests have to be rewritten

* Move peer hashmap to `SyncingEngine`

* Let `SyncingEngine` to implement `ChainSyncInterface`

* Introduce `SyncStatusProvider`

* Move `sync_peer_(connected|disconnected)` to `SyncingEngine`

* Implement `SyncEventStream`

Remove `SyncConnected`/`SyncDisconnected` events from
`NetworkEvenStream` and provide those events through
`ChainSyncInterface` instead.

Modify BEEFY/GRANDPA/transactions protocol and `NetworkGossip` to take
`SyncEventStream` object which they listen to for incoming sync peer
events.

* Introduce `ChainSyncInterface`

This interface provides a set of miscellaneous functions that other
subsystems can use to query, for example, the syncing status.

* Move event stream polling to `SyncingEngine`

Subscribe to `NetworkStreamEvent` and poll the incoming notifications
and substream events from `SyncingEngine`.

The code needs refactoring.

* Make `SyncingEngine` into an asynchronous runner

This commits removes the last hard dependency of syncing from
`sc-network` meaning the protocol now lives completely outside of
`sc-network`, ignoring the hardcoded peerset entry which will be
addressed in the future.

Code needs a lot of refactoring.

* Fix warnings

* Code refactoring

* Use `SyncingService` for BEEFY

* Use `SyncingService` for GRANDPA

* Remove call delegation from `NetworkService`

* Remove `ChainSyncService`

* Remove `ChainSync` service tests

They were written for the sole purpose of verifying that `NetworWorker`
continues to function while the calls are being dispatched to
`ChainSync`.

* Refactor code

* Refactor code

* Update client/finality-grandpa/src/communication/tests.rs

Co-authored-by: Anton <anton.kalyaev@gmail.com>

* Fix warnings

* Apply review comments

* Fix docs

* Fix test

* cargo-fmt

* Update client/network/sync/src/engine.rs

Co-authored-by: Anton <anton.kalyaev@gmail.com>

* Update client/network/sync/src/engine.rs

Co-authored-by: Anton <anton.kalyaev@gmail.com>

* Add missing docs

* Refactor code

---------

Co-authored-by: Anton <anton.kalyaev@gmail.com>

substrate/client/consensus/beefy/src/tests.rs

@@ -223,6 +223,10 @@ impl TestNetFactory for BeefyTestNet {
 		&self.peers
 	}
 
+	fn peers_mut(&mut self) -> &mut Vec<BeefyPeer> {
+		&mut self.peers
+	}
+
 	fn mut_peers<F: FnOnce(&mut Vec<BeefyPeer>)>(&mut self, closure: F) {
 		closure(&mut self.peers);
 	}
@@ -353,6 +357,7 @@ async fn voter_init_setup(
 		Arc::new(crate::communication::gossip::GossipValidator::new(known_peers));
 	let mut gossip_engine = sc_network_gossip::GossipEngine::new(
 		net.peer(0).network_service().clone(),
+		net.peer(0).sync_service().clone(),
 		"/beefy/whatever",
 		gossip_validator,
 		None,
@@ -389,6 +394,7 @@ where
 
 		let network_params = crate::BeefyNetworkParams {
 			network: peer.network_service().clone(),
+			sync: peer.sync_service().clone(),
 			gossip_protocol_name: beefy_gossip_proto_name(),
 			justifications_protocol_name: on_demand_justif_handler.protocol_name(),
 			_phantom: PhantomData,
@@ -407,7 +413,7 @@ where
 			prometheus_registry: None,
 			on_demand_justifications_handler: on_demand_justif_handler,
 		};
-		let task = crate::start_beefy_gadget::<_, _, _, _, _, _>(beefy_params);
+		let task = crate::start_beefy_gadget::<_, _, _, _, _, _, _>(beefy_params);
 
 		fn assert_send<T: Send>(_: &T) {}
 		assert_send(&task);