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/bin/node-template/node/src/service.rs

@@ -192,7 +192,7 @@ pub fn new_full(mut config: Configuration) -> Result<TaskManager, ServiceError>
 		Vec::default(),
 	));
 
-	let (network, system_rpc_tx, tx_handler_controller, network_starter) =
+	let (network, system_rpc_tx, tx_handler_controller, network_starter, sync_service) =
 		sc_service::build_network(sc_service::BuildNetworkParams {
 			config: &config,
 			client: client.clone(),
@@ -240,6 +240,7 @@ pub fn new_full(mut config: Configuration) -> Result<TaskManager, ServiceError>
 		backend,
 		system_rpc_tx,
 		tx_handler_controller,
+		sync_service: sync_service.clone(),
 		config,
 		telemetry: telemetry.as_mut(),
 	})?;
@@ -276,8 +277,8 @@ pub fn new_full(mut config: Configuration) -> Result<TaskManager, ServiceError>
 				force_authoring,
 				backoff_authoring_blocks,
 				keystore: keystore_container.sync_keystore(),
-				sync_oracle: network.clone(),
-				justification_sync_link: network.clone(),
+				sync_oracle: sync_service.clone(),
+				justification_sync_link: sync_service.clone(),
 				block_proposal_slot_portion: SlotProportion::new(2f32 / 3f32),
 				max_block_proposal_slot_portion: None,
 				telemetry: telemetry.as_ref().map(|x| x.handle()),
@@ -320,6 +321,7 @@ pub fn new_full(mut config: Configuration) -> Result<TaskManager, ServiceError>
 			config: grandpa_config,
 			link: grandpa_link,
 			network,
+			sync: Arc::new(sync_service),
 			voting_rule: sc_consensus_grandpa::VotingRulesBuilder::default().build(),
 			prometheus_registry,
 			shared_voter_state: SharedVoterState::empty(),