Check that the validation code matches the parachain code (#3433)

This introduces a check to ensure that the parachain code matches the
validation code stored in the relay chain state. If not, it will print a
warning. This should be mainly useful for parachain builders to make
sure they have setup everything correctly.

cumulus/client/network/src/tests.rs

@@ -117,6 +117,15 @@ impl RelayChainInterface for DummyRelayChainInterface {
 		}))
 	}
 
+	async fn validation_code_hash(
+		&self,
+		_: PHash,
+		_: ParaId,
+		_: OccupiedCoreAssumption,
+	) -> RelayChainResult<Option<ValidationCodeHash>> {
+		unimplemented!("Not needed for test")
+	}
+
 	async fn candidate_pending_availability(
 		&self,
 		_: PHash,