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/rpc/src/dev/mod.rs

@@ -87,7 +87,7 @@ where
 			let parent_hash = *block.header().parent_hash();
 			let parent_header = self
 				.client
-				.header(BlockId::Hash(parent_hash))
+				.header(parent_hash)
 				.map_err(|e| Error::BlockQueryError(Box::new(e)))?;
 			if let Some(header) = parent_header {
 				header