BlockId removal: refactor: HeaderBackend::header (#12874)

* BlockId removal: refactor: HeaderBackend::header

It changes the arguments of:
- `HeaderBackend::header`,
- `Client::header`,
- `PeersClient::header`
- `ChainApi::block_header`

methods from: `BlockId<Block>` to: `Block::Hash`

This PR is part of BlockId::Number refactoring analysis (paritytech/substrate#11292)

* non-trivial usages of haeder(block_id) refactored

This may required introduction of dedicated function:
header_for_block_num

* fmt

* fix

* doc fixed

* ".git/.scripts/fmt.sh"

* BlockId removal: refactor: HeaderBackend::expect_header

It changes the arguments of `HeaderBackend::expect_header` method from: `BlockId<Block>` to: `Block::Hash`

* ".git/.scripts/fmt.sh"

* readme updated

* ".git/.scripts/fmt.sh"

* fix

Co-authored-by: parity-processbot <>

substrate/client/network/test/src/block_import.rs

@@ -26,7 +26,6 @@ use sc_consensus::{
 	IncomingBlock,
 };
 use sp_consensus::BlockOrigin;
-use sp_runtime::generic::BlockId;
 use substrate_test_runtime_client::{
 	self,
 	prelude::*,
@@ -39,7 +38,7 @@ fn prepare_good_block() -> (TestClient, Hash, u64, PeerId, IncomingBlock<Block>)
 	block_on(client.import(BlockOrigin::File, block)).unwrap();
 
 	let (hash, number) = (client.block_hash(1).unwrap().unwrap(), 1);
-	let header = client.header(&BlockId::Number(1)).unwrap();
+	let header = client.header(hash).unwrap();
 	let justifications = client.justifications(hash).unwrap();
 	let peer_id = PeerId::random();
 	(