Move import queue out of sc-network (#12764)

* 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.

* Fix tests

* Apply review comments

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <git@kchr.de>

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

Co-authored-by: Bastian Köcher <git@kchr.de>

Co-authored-by: Bastian Köcher <git@kchr.de>

substrate/client/network/src/lib.rs

@@ -258,6 +258,7 @@ pub mod network_state;
 #[doc(inline)]
 pub use libp2p::{multiaddr, Multiaddr, PeerId};
 pub use protocol::PeerInfo;
+use sc_consensus::{JustificationSyncLink, Link};
 pub use sc_network_common::{
 	protocol::{
 		event::{DhtEvent, Event},
@@ -297,11 +298,15 @@ const MAX_CONNECTIONS_ESTABLISHED_INCOMING: u32 = 10_000;
 
 /// Abstraction over syncing-related services
 pub trait ChainSyncInterface<B: BlockT>:
-	NetworkSyncForkRequest<B::Hash, NumberFor<B>> + Send + Sync
+	NetworkSyncForkRequest<B::Hash, NumberFor<B>> + JustificationSyncLink<B> + Link<B> + Send + Sync
 {
 }
 
 impl<T, B: BlockT> ChainSyncInterface<B> for T where
-	T: NetworkSyncForkRequest<B::Hash, NumberFor<B>> + Send + Sync
+	T: NetworkSyncForkRequest<B::Hash, NumberFor<B>>
+		+ JustificationSyncLink<B>
+		+ Link<B>
+		+ Send
+		+ Sync
 {
 }