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/block_request_handler.rs

@@ -330,7 +330,16 @@ where
 		let mut blocks = Vec::new();
 
 		let mut total_size: usize = 0;
-		while let Some(header) = self.client.header(block_id).unwrap_or_default() {
+
+		let client_header_from_block_id =
+			|block_id: BlockId<B>| -> Result<Option<B::Header>, HandleRequestError> {
+				if let Some(hash) = self.client.block_hash_from_id(&block_id)? {
+					return self.client.header(hash).map_err(Into::into)
+				}
+				Ok(None)
+			};
+
+		while let Some(header) = client_header_from_block_id(block_id).unwrap_or_default() {
 			let number = *header.number();
 			let hash = header.hash();
 			let parent_hash = *header.parent_hash();