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/network/src/service/metrics.rs

@@ -24,7 +24,7 @@ use prometheus_endpoint::{
 use std::{
 	str,
 	sync::{
-		atomic::{AtomicBool, AtomicUsize, Ordering},
+		atomic::{AtomicUsize, Ordering},
 		Arc,
 	},
 };
@@ -34,7 +34,6 @@ pub use prometheus_endpoint::{Histogram, HistogramVec};
 /// Registers all networking metrics with the given registry.
 pub fn register(registry: &Registry, sources: MetricSources) -> Result<Metrics, PrometheusError> {
 	BandwidthCounters::register(registry, sources.bandwidth)?;
-	MajorSyncingGauge::register(registry, sources.major_syncing)?;
 	NumConnectedGauge::register(registry, sources.connected_peers)?;
 	Metrics::register(registry)
 }
@@ -42,7 +41,6 @@ pub fn register(registry: &Registry, sources: MetricSources) -> Result<Metrics,
 /// Predefined metric sources that are fed directly into prometheus.
 pub struct MetricSources {
 	pub bandwidth: Arc<BandwidthSinks>,
-	pub major_syncing: Arc<AtomicBool>,
 	pub connected_peers: Arc<AtomicUsize>,
 }
 
@@ -266,37 +264,6 @@ impl MetricSource for BandwidthCounters {
 	}
 }
 
-/// The "major syncing" metric.
-#[derive(Clone)]
-pub struct MajorSyncingGauge(Arc<AtomicBool>);
-
-impl MajorSyncingGauge {
-	/// Registers the `MajorSyncGauge` metric whose value is
-	/// obtained from the given `AtomicBool`.
-	fn register(registry: &Registry, value: Arc<AtomicBool>) -> Result<(), PrometheusError> {
-		prometheus::register(
-			SourcedGauge::new(
-				&Opts::new(
-					"substrate_sub_libp2p_is_major_syncing",
-					"Whether the node is performing a major sync or not.",
-				),
-				MajorSyncingGauge(value),
-			)?,
-			registry,
-		)?;
-
-		Ok(())
-	}
-}
-
-impl MetricSource for MajorSyncingGauge {
-	type N = u64;
-
-	fn collect(&self, mut set: impl FnMut(&[&str], Self::N)) {
-		set(&[], self.0.load(Ordering::Relaxed) as u64);
-	}
-}
-
 /// The connected peers metric.
 #[derive(Clone)]
 pub struct NumConnectedGauge(Arc<AtomicUsize>);