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/consensus/common/src/longest_chain.rs

@@ -21,10 +21,7 @@
 use sc_client_api::backend;
 use sp_blockchain::{Backend, HeaderBackend};
 use sp_consensus::{Error as ConsensusError, SelectChain};
-use sp_runtime::{
-	generic::BlockId,
-	traits::{Block as BlockT, NumberFor},
-};
+use sp_runtime::traits::{Block as BlockT, NumberFor};
 use std::{marker::PhantomData, sync::Arc};
 
 /// Implement Longest Chain Select implementation
@@ -63,7 +60,7 @@ where
 		Ok(self
 			.backend
 			.blockchain()
-			.header(BlockId::Hash(best_hash))?
+			.header(best_hash)?
 			.expect("given block hash was fetched from block in db; qed"))
 	}