Custom RPC for Merkle Mountain Range pallet (#8137)

* Add MMR custom RPC.

* Change RuntimeApi to avoid hardcoding leaf type.

* Properly implement the new RuntimeAPI and wire up RPC.

* Extract Offchain DB as separate execution extension.

* Enable offchain DB access for offchain calls.

* Fix offchain_election tests.

* Skip block initialisation for proof generation.

* Fix integration test setup.

* Fix offchain tests. Not sure how I missed them earlier 🤷.

* Fix long line.

* One more test missing.

* Update mock for multi-phase.

* Address review grumbbles.

* Address review grumbles.

* Fix line width of a comment

substrate/bin/node/rpc/src/lib.rs

@@ -116,6 +116,7 @@ pub fn create_full<C, P, SC, B>(
 		HeaderMetadata<Block, Error=BlockChainError> + Sync + Send + 'static,
 	C::Api: substrate_frame_rpc_system::AccountNonceApi<Block, AccountId, Index>,
 	C::Api: pallet_contracts_rpc::ContractsRuntimeApi<Block, AccountId, Balance, BlockNumber>,
+	C::Api: pallet_mmr_rpc::MmrRuntimeApi<Block, <Block as sp_runtime::traits::Block>::Hash>,
 	C::Api: pallet_transaction_payment_rpc::TransactionPaymentRuntimeApi<Block, Balance>,
 	C::Api: BabeApi<Block>,
 	C::Api: BlockBuilder<Block>,
@@ -126,6 +127,7 @@ pub fn create_full<C, P, SC, B>(
 {
 	use substrate_frame_rpc_system::{FullSystem, SystemApi};
 	use pallet_contracts_rpc::{Contracts, ContractsApi};
+	use pallet_mmr_rpc::{MmrApi, Mmr};
 	use pallet_transaction_payment_rpc::{TransactionPayment, TransactionPaymentApi};
 
 	let mut io = jsonrpc_core::IoHandler::default();
@@ -161,6 +163,9 @@ pub fn create_full<C, P, SC, B>(
 	io.extend_with(
 		ContractsApi::to_delegate(Contracts::new(client.clone()))
 	);
+	io.extend_with(
+		MmrApi::to_delegate(Mmr::new(client.clone()))
+	);
 	io.extend_with(
 		TransactionPaymentApi::to_delegate(TransactionPayment::new(client.clone()))
 	);