Move sc-client into sc-service (#5502)

* Drop client from sc-network and sc-client-db, move LongestChain to sc-client-api

* move leaves, cht, in_mem to sc-client-api, drop client from sc-finality-grandpa

* drop sc-service from sc-rpc

* drop sc-service from sc-consensus-aura

* drop sc-client from manual-seal and babe

* drop sc-client from utils/frame/rpc/system and utils/frame/benchmarking-cli

* drop sc-client from bin/node and bin/node-template

* drop sc-client

* fix tests

* remove check -p sc-client from gitlab.yml

* fix warnings

* fixes ui test

* fix light client tests

* adds associated Client type to AbstractService

* adds UsageProvider to Client

* fixed ui test, again

* tried and failed to get node-cli to compile for wasm

* thanks to tomaka for helping me get node-cli to compile for wasmm

* ui test pls pas 🙏🏾

* all tests passing 🪄

* no_run documentation code

* rm -f documentation code

* ClientProvider

* fix mega trait

* move LongestChain to sc-consensus, use adds minimal bounds to AbstractService::Client

* adds license to sc-consensus

Co-authored-by: Benjamin Kampmann <ben@parity.io>

substrate/client/api/src/light.rs

@@ -296,7 +296,25 @@ pub trait RemoteBlockchain<Block: BlockT>: Send + Sync {
 	>>;
 }
 
+/// Returns future that resolves header either locally, or remotely.
+pub fn future_header<Block: BlockT, F: Fetcher<Block>>(
+	blockchain: &dyn RemoteBlockchain<Block>,
+	fetcher: &F,
+	id: BlockId<Block>,
+) -> impl Future<Output = Result<Option<Block::Header>, ClientError>> {
+	use futures::future::{ready, Either, FutureExt};
 
+	match blockchain.header(id) {
+		Ok(LocalOrRemote::Remote(request)) => Either::Left(
+			fetcher
+				.remote_header(request)
+				.then(|header| ready(header.map(Some)))
+		),
+		Ok(LocalOrRemote::Unknown) => Either::Right(ready(Ok(None))),
+		Ok(LocalOrRemote::Local(local_header)) => Either::Right(ready(Ok(Some(local_header)))),
+		Err(err) => Either::Right(ready(Err(err))),
+	}
+}
 
 #[cfg(test)]
 pub mod tests {