Network sync refactoring (part 3) (#11347)

* Move `light.v1.proto` schema into new crate `sc-network-light`

* Move `sc_network::light_client_requests` and submodule to `sc_network_light::light_client_requests`

* Fix apparently outdated reference in documentation and visibility modifier

* Fix rustdoc check

* Update lock file

substrate/client/network/light/src/lib.rs

@@ -0,0 +1,22 @@
+// 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/>.
+
+//! Light client data structures of the networking layer.
+
+pub mod light_client_requests;
+mod schema;