Extract warp sync strategy from ChainSync (#2467)

Extract `WarpSync` (and `StateSync` as part of warp sync) from
`ChainSync` as independent syncing strategy called by `SyncingEngine`.
Introduce `SyncingStrategy` enum as a proxy between `SyncingEngine` and
specific syncing strategies.

## Limitations
Gap sync is kept in `ChainSync` for now because it shares the same set
of peers as block syncing implementation in `ChainSync`. Extraction of a
common context responsible for peer management in syncing strategies
able to run in parallel is planned for a follow-up PR.

## Further improvements
A possibility of conversion of `SyncingStartegy` into a trait should be
evaluated. The main stopper for this is that different strategies need
to communicate different actions to `SyncingEngine` and respond to
different events / provide different APIs (e.g., requesting
justifications is only possible via `ChainSync` and not through
`WarpSync`; `SendWarpProofRequest` action is only relevant to
`WarpSync`, etc.)

---------

Co-authored-by: Aaro Altonen <48052676+altonen@users.noreply.github.com>

substrate/client/informant/src/display.rs

@@ -21,10 +21,7 @@ use ansi_term::Colour;
 use log::info;
 use sc_client_api::ClientInfo;
 use sc_network::NetworkStatus;
-use sc_network_sync::{
-	warp::{WarpSyncPhase, WarpSyncProgress},
-	SyncState, SyncStatus,
-};
+use sc_network_sync::{SyncState, SyncStatus, WarpSyncPhase, WarpSyncProgress};
 use sp_runtime::traits::{Block as BlockT, CheckedDiv, NumberFor, Saturating, Zero};
 use std::{fmt, time::Instant};
 
@@ -130,9 +127,10 @@ impl<B: BlockT> InformantDisplay<B> {
 					),
 				(_, Some(state), _) => (
 					"⚙️ ",
-					"Downloading state".into(),
+					"State sync".into(),
 					format!(
-						", {}%, {:.2} Mib",
+						", {}, {}%, {:.2} Mib",
+						state.phase,
 						state.percentage,
 						(state.size as f32) / (1024f32 * 1024f32)
 					),