Network sync refactoring (part 4) (#11412)

* Remove direct dependency of `sc-network` on `sc-network-light`

* Move `WarpSyncProvider` trait and surrounding data structures into `sc-network-common`

* Move `WarpSyncProvider` trait and surrounding data structures into `sc-network-common`

* Create `sync` module in `sc-network-common`, create `ChainSync` trait there (not used yet), move a bunch of associated data structures from `sc-network-sync`

* Switch from concrete implementation to `ChainSync` trait from `sc-network-common`

* Introduce `OpaqueStateRequest`/`OpaqueStateResponse` to remove generics from `StateSync` trait

* Introduce `OpaqueBlockRequest`/`OpaqueBlockResponse`, make `scheme` module of `sc-network-sync` private

* Surface `sc-network-sync` into `sc-service` and make `sc-network` not depend on it anymore

* Remove now unnecessary dependency from `sc-network`

* Replace crate links with just text since dependencies are gone now

* Remove `warp_sync` re-export from `sc-network-common`

* Update copyright in network-related files

* Address review comments about documentation

* Apply review suggestion

* Rename `extra_requests` module to `metrics`

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

substrate/client/network/common/src/sync/metrics.rs

@@ -0,0 +1,25 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2017-2022 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/>.
+
+#[derive(Debug)]
+pub struct Metrics {
+	pub pending_requests: u32,
+	pub active_requests: u32,
+	pub importing_requests: u32,
+	pub failed_requests: u32,
+}