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/sync/src/lib.rs

@@ -1082,7 +1082,7 @@ where
 				heads.sort();
 				let median = heads[heads.len() / 2];
 				if number + STATE_SYNC_FINALITY_THRESHOLD.saturated_into() >= median {
-					if let Ok(Some(header)) = self.client.header(BlockId::hash(*hash)) {
+					if let Ok(Some(header)) = self.client.header(*hash) {
 						log::debug!(
 							target: "sync",
 							"Starting state sync for #{} ({})",