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/consensus/common/src/import_queue/mock.rs

@@ -0,0 +1,46 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2022 Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+use super::*;
+
+mockall::mock! {
+	pub ImportQueueHandle<B: BlockT> {}
+
+	impl<B: BlockT> ImportQueueService<B> for ImportQueueHandle<B> {
+		fn import_blocks(&mut self, origin: BlockOrigin, blocks: Vec<IncomingBlock<B>>);
+		fn import_justifications(
+			&mut self,
+			who: RuntimeOrigin,
+			hash: B::Hash,
+			number: NumberFor<B>,
+			justifications: Justifications,
+		);
+	}
+}
+
+mockall::mock! {
+	pub ImportQueue<B: BlockT> {}
+
+	#[async_trait::async_trait]
+	impl<B: BlockT> ImportQueue<B> for ImportQueue<B> {
+		fn service(&self) -> Box<dyn ImportQueueService<B>>;
+		fn service_ref(&mut self) -> &mut dyn ImportQueueService<B>;
+		fn poll_actions<'a>(&mut self, cx: &mut futures::task::Context<'a>, link: &mut dyn Link<B>);
+		async fn run(self, link: Box<dyn Link<B>>);
+	}
+}