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/utils/frame/benchmarking-cli/src/command.rs

@@ -26,7 +26,7 @@ use sp_state_machine::StateMachine;
 use sp_externalities::Extensions;
 use sc_service::{Configuration, NativeExecutionDispatch};
 use sp_runtime::traits::{Block as BlockT, Header as HeaderT, NumberFor};
-use sp_core::offchain::{OffchainExt, testing::TestOffchainExt};
+use sp_core::offchain::{OffchainWorkerExt, testing::TestOffchainExt};
 use sp_keystore::{
 	SyncCryptoStorePtr, KeystoreExt,
 	testing::KeyStore,
@@ -73,7 +73,7 @@ impl BenchmarkCmd {
 		let mut extensions = Extensions::default();
 		extensions.register(KeystoreExt(Arc::new(KeyStore::new()) as SyncCryptoStorePtr));
 		let (offchain, _) = TestOffchainExt::new();
-		extensions.register(OffchainExt::new(offchain));
+		extensions.register(OffchainWorkerExt::new(offchain));
 
 		let result = StateMachine::<_, _, NumberFor<BB>, _>::new(
 			&state,