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/grandpa/src/environment.rs

@@ -50,7 +50,7 @@ use sp_runtime::traits::{Block as BlockT, Header as HeaderT, NumberFor, Zero};
 
 use crate::{
 	authorities::{AuthoritySet, SharedAuthoritySet},
-	communication::Network as NetworkT,
+	communication::{Network as NetworkT, Syncing as SyncingT},
 	justification::GrandpaJustification,
 	local_authority_id,
 	notification::GrandpaJustificationSender,
@@ -423,13 +423,21 @@ impl Metrics {
 }
 
 /// The environment we run GRANDPA in.
-pub(crate) struct Environment<Backend, Block: BlockT, C, N: NetworkT<Block>, SC, VR> {
+pub(crate) struct Environment<
+	Backend,
+	Block: BlockT,
+	C,
+	N: NetworkT<Block>,
+	S: SyncingT<Block>,
+	SC,
+	VR,
+> {
 	pub(crate) client: Arc<C>,
 	pub(crate) select_chain: SC,
 	pub(crate) voters: Arc<VoterSet<AuthorityId>>,
 	pub(crate) config: Config,
 	pub(crate) authority_set: SharedAuthoritySet<Block::Hash, NumberFor<Block>>,
-	pub(crate) network: crate::communication::NetworkBridge<Block, N>,
+	pub(crate) network: crate::communication::NetworkBridge<Block, N, S>,
 	pub(crate) set_id: SetId,
 	pub(crate) voter_set_state: SharedVoterSetState<Block>,
 	pub(crate) voting_rule: VR,
@@ -439,7 +447,9 @@ pub(crate) struct Environment<Backend, Block: BlockT, C, N: NetworkT<Block>, SC,
 	pub(crate) _phantom: PhantomData<Backend>,
 }
 
-impl<BE, Block: BlockT, C, N: NetworkT<Block>, SC, VR> Environment<BE, Block, C, N, SC, VR> {
+impl<BE, Block: BlockT, C, N: NetworkT<Block>, S: SyncingT<Block>, SC, VR>
+	Environment<BE, Block, C, N, S, SC, VR>
+{
 	/// Updates the voter set state using the given closure. The write lock is
 	/// held during evaluation of the closure and the environment's voter set
 	/// state is set to its result if successful.
@@ -469,13 +479,14 @@ impl<BE, Block: BlockT, C, N: NetworkT<Block>, SC, VR> Environment<BE, Block, C,
 	}
 }
 
-impl<BE, Block, C, N, SC, VR> Environment<BE, Block, C, N, SC, VR>
+impl<BE, Block, C, N, S, SC, VR> Environment<BE, Block, C, N, S, SC, VR>
 where
 	Block: BlockT,
 	BE: BackendT<Block>,
 	C: ClientForGrandpa<Block, BE>,
 	C::Api: GrandpaApi<Block>,
 	N: NetworkT<Block>,
+	S: SyncingT<Block>,
 	SC: SelectChainT<Block>,
 {
 	/// Report the given equivocation to the GRANDPA runtime module. This method
@@ -572,13 +583,14 @@ where
 	}
 }
 
-impl<BE, Block, C, N, SC, VR> finality_grandpa::Chain<Block::Hash, NumberFor<Block>>
-	for Environment<BE, Block, C, N, SC, VR>
+impl<BE, Block, C, N, S, SC, VR> finality_grandpa::Chain<Block::Hash, NumberFor<Block>>
+	for Environment<BE, Block, C, N, S, SC, VR>
 where
 	Block: BlockT,
 	BE: BackendT<Block>,
 	C: ClientForGrandpa<Block, BE>,
 	N: NetworkT<Block>,
+	S: SyncingT<Block>,
 	SC: SelectChainT<Block>,
 	VR: VotingRuleT<Block, C>,
 	NumberFor<Block>: BlockNumberOps,
@@ -630,14 +642,15 @@ where
 	Ok(tree_route.retracted().iter().skip(1).map(|e| e.hash).collect())
 }
 
-impl<B, Block, C, N, SC, VR> voter::Environment<Block::Hash, NumberFor<Block>>
-	for Environment<B, Block, C, N, SC, VR>
+impl<B, Block, C, N, S, SC, VR> voter::Environment<Block::Hash, NumberFor<Block>>
+	for Environment<B, Block, C, N, S, SC, VR>
 where
 	Block: BlockT,
 	B: BackendT<Block>,
 	C: ClientForGrandpa<Block, B> + 'static,
 	C::Api: GrandpaApi<Block>,
 	N: NetworkT<Block>,
+	S: SyncingT<Block>,
 	SC: SelectChainT<Block> + 'static,
 	VR: VotingRuleT<Block, C> + Clone + 'static,
 	NumberFor<Block>: BlockNumberOps,