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/network/test/src/lib.rs

@@ -66,7 +66,7 @@ use sc_network_sync::{
 	block_request_handler::BlockRequestHandler,
 	service::{network::NetworkServiceProvider, syncing_service::SyncingService},
 	state_request_handler::StateRequestHandler,
-	warp::{
+	strategy::warp::{
 		AuthorityList, EncodedProof, SetId, VerificationResult, WarpSyncParams, WarpSyncProvider,
 	},
 	warp_request_handler,
@@ -699,6 +699,8 @@ pub struct FullPeerConfig {
 	pub storage_chain: bool,
 	/// Optional target block header to sync to
 	pub target_block: Option<<Block as BlockT>::Header>,
+	/// Force genesis even in case of warp & light state sync.
+	pub force_genesis: bool,
 }
 
 #[async_trait::async_trait]
@@ -758,7 +760,9 @@ pub trait TestNetFactory: Default + Sized + Send {
 			*genesis_extra_storage = storage;
 		}
 
-		if matches!(config.sync_mode, SyncMode::LightState { .. } | SyncMode::Warp) {
+		if !config.force_genesis &&
+			matches!(config.sync_mode, SyncMode::LightState { .. } | SyncMode::Warp)
+		{
 			test_client_builder = test_client_builder.set_no_genesis();
 		}
 		let backend = test_client_builder.backend();