Replace BATCH_CALL_SUPPORTED (#1733)

* Simplify submit_and_watch_signed_extrinsic

The way submit_and_watch_signed_extrinsic is used now, we can always
derive the SignParam from other params. If in the future we need more
customization possibilities, we can define a new method.

* Simplify submit_signed_extrinsic

* Send maybe_batch_tx as a parameter

Send `maybe_batch_tx` as a parameter to `submit_proof()`. This way we
can deduplicate the logic that submits the extrinsic for
`messages_source and `messages_target` and we can simplify the logic in
the race loop a bit.

* Define BatchProofTransaction

Deduplicate BatchConfirmationTransaction and BatchDeliveryTransaction by
replacing both of them with BatchProofTransaction

* Define ChainWithUtilityPallet and BatchCallBuilderConstructor

- Define `ChainWithUtilityPallet` in order to be able to associate the
  batching functionality with chains
- Defining `BatchCallBuilderConstructor` in order to have a more reliable
  way of checking whether an end of a messages pipeline supports batching
  or no. `BatchCallBuilderConstructor::new_builder()` returns an
  `Option<BatchCallBuilder>`.This is a bit safer because each time a caller
  tries to start creating a batch call, it will call `new_builder()` and
  will be required to handle the returned `Option`. Before we only had a
  bool `BATCH_CALL_SUPPORTED` the caller could have forgetten to check.

bridges/relays/client-millau/src/lib.rs

@@ -20,8 +20,8 @@ use bp_messages::MessageNonce;
 use codec::{Compact, Decode, Encode};
 use relay_substrate_client::{
 	BalanceOf, Chain, ChainWithBalances, ChainWithGrandpa, ChainWithMessages,
-	ChainWithTransactions, Error as SubstrateError, IndexOf, SignParam, UnderlyingChainProvider,
-	UnsignedTransaction,
+	ChainWithTransactions, ChainWithUtilityPallet, Error as SubstrateError,
+	FullRuntimeUtilityPallet, IndexOf, SignParam, UnderlyingChainProvider, UnsignedTransaction,
 };
 use sp_core::{storage::StorageKey, Pair};
 use sp_runtime::{generic::SignedPayload, traits::IdentifyAccount};
@@ -149,6 +149,10 @@ impl ChainWithTransactions for Millau {
 	}
 }
 
+impl ChainWithUtilityPallet for Millau {
+	type UtilityPallet = FullRuntimeUtilityPallet<millau_runtime::Runtime>;
+}
+
 /// Millau signing params.
 pub type SigningParams = sp_core::sr25519::Pair;