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/test-utils/test-runner/src/client.rs

@@ -192,7 +192,7 @@ where
 			rpc_extensions_builder: Box::new(move |_, _| {
 				let mut io = jsonrpc_core::IoHandler::default();
 				io.extend_with(ManualSealApi::to_delegate(ManualSeal::new(rpc_sink.clone())));
-				io
+				Ok(io)
 			}),
 			remote_blockchain: None,
 			network,