Decouples light-sync state from chain spec (#9491)

* Decouples light-sync state from chain spec

This decouples the light-sync state from chain spec. First, the
light-sync state currently only works with BABE+Grandpa, so not
all *Substrate* based chains can use this feature. The next problem was
also that this pulled the `sc-consensus-babe` and `sc-finality-grandpa`
crate into `sc-chain-spec`.

If a chain now wants to support the light-sync state, it needs to add
the `LightSyncStateExtension` to the chain spec as an extension. This is
documented in the crate level docs of `sc-sync-state-rpc`. If this
extension is not available, `SyncStateRpc` fails at initialization.

* Fix compilation for browser

* Fmt

substrate/bin/node/rpc/src/lib.rs

@@ -111,7 +111,7 @@ pub type IoHandler = jsonrpc_core::IoHandler<sc_rpc::Metadata>;
 /// Instantiate all Full RPC extensions.
 pub fn create_full<C, P, SC, B>(
 	deps: FullDeps<C, P, SC, B>,
-) -> jsonrpc_core::IoHandler<sc_rpc_api::Metadata>
+) -> Result<jsonrpc_core::IoHandler<sc_rpc_api::Metadata>, Box<dyn std::error::Error + Send + Sync>>
 where
 	C: ProvideRuntimeApi<Block>
 		+ HeaderBackend<Block>
@@ -178,10 +178,10 @@ where
 			shared_authority_set,
 			shared_epoch_changes,
 			deny_unsafe,
-		),
+		)?,
 	));
 
-	io
+	Ok(io)
 }
 
 /// Instantiate all Light RPC extensions.