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/finality-grandpa/src/justification.rs

@@ -26,10 +26,7 @@ use finality_grandpa::{voter_set::VoterSet, Error as GrandpaError};
 use parity_scale_codec::{Decode, Encode};
 use sp_blockchain::{Error as ClientError, HeaderBackend};
 use sp_finality_grandpa::AuthorityId;
-use sp_runtime::{
-	generic::BlockId,
-	traits::{Block as BlockT, Header as HeaderT, NumberFor},
-};
+use sp_runtime::traits::{Block as BlockT, Header as HeaderT, NumberFor};
 
 use crate::{AuthorityList, Commit, Error};
 
@@ -104,7 +101,7 @@ impl<Block: BlockT> GrandpaJustification<Block> {
 					break
 				}
 
-				match client.header(BlockId::Hash(current_hash))? {
+				match client.header(current_hash)? {
 					Some(current_header) => {
 						// NOTE: this should never happen as we pick the lowest block
 						// as base and only traverse backwards from the other blocks