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/babe/src/lib.rs

@@ -1425,7 +1425,7 @@ where
 		let parent_hash = *block.header.parent_hash();
 		let parent_header = self
 			.client
-			.header(BlockId::Hash(parent_hash))
+			.header(parent_hash)
 			.map_err(|e| ConsensusError::ChainLookup(e.to_string()))?
 			.ok_or_else(|| {
 				ConsensusError::ChainLookup(
@@ -1664,7 +1664,7 @@ where
 
 	let finalized_slot = {
 		let finalized_header = client
-			.header(BlockId::Hash(info.finalized_hash))
+			.header(info.finalized_hash)
 			.map_err(|e| ConsensusError::ClientImport(e.to_string()))?
 			.expect(
 				"best finalized hash was given by client; finalized headers must exist in db; qed",