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/import.rs

@@ -122,7 +122,7 @@ where
 				};
 
 				if let Ok(hash) = effective_block_hash {
-					if let Ok(Some(header)) = self.inner.header(BlockId::Hash(hash)) {
+					if let Ok(Some(header)) = self.inner.header(hash) {
 						if *header.number() == pending_change.effective_number() {
 							out.push((header.hash(), *header.number()));
 						}
@@ -364,14 +364,12 @@ where
 					// best finalized block.
 					let best_finalized_number = self.inner.info().finalized_number;
 					let canon_number = best_finalized_number.min(median_last_finalized_number);
-					let canon_hash =
-						self.inner.header(BlockId::Number(canon_number))
+					let canon_hash = self.inner.hash(canon_number)
 							.map_err(|e| ConsensusError::ClientImport(e.to_string()))?
 							.expect(
 								"the given block number is less or equal than the current best finalized number; \
 								 current best finalized number must exist in chain; qed."
-							)
-							.hash();
+							);
 
 					NewAuthoritySet {
 						canon_number,