Deduplicate pallet call structs used for indirect runtime calls (#1744)

* Small changes

* Define generic bridge pallets call structs

* polkadot-core SignedExtension simplifications

- we don't seem to need to pass the Call as a generic param
- we can use codec(skip) instead of implementing Encode and Decode

* Split BridgeHubRococo and BridgeHubWococo calls

* code review fixes

bridges/modules/grandpa/src/lib.rs

@@ -612,6 +612,7 @@ mod tests {
 		run_test, test_header, RuntimeOrigin, TestHeader, TestNumber, TestRuntime,
 		MAX_BRIDGED_AUTHORITIES,
 	};
+	use bp_header_chain::BridgeGrandpaCall;
 	use bp_runtime::BasicOperatingMode;
 	use bp_test_utils::{
 		authority_list, generate_owned_bridge_module_tests, make_default_justification,
@@ -1160,5 +1161,33 @@ mod tests {
 		);
 	}
 
+	#[test]
+	fn test_bridge_grandpa_call_is_correctly_defined() {
+		let header = test_header(0);
+		let init_data = InitializationData {
+			header: Box::new(header.clone()),
+			authority_list: authority_list(),
+			set_id: 1,
+			operating_mode: BasicOperatingMode::Normal,
+		};
+		let justification = make_default_justification(&header);
+
+		let direct_initialize_call =
+			Call::<TestRuntime>::initialize { init_data: init_data.clone() };
+		let indirect_initialize_call = BridgeGrandpaCall::<TestHeader>::initialize(init_data);
+		assert_eq!(direct_initialize_call.encode(), indirect_initialize_call.encode());
+
+		let direct_submit_finality_proof_call = Call::<TestRuntime>::submit_finality_proof {
+			finality_target: Box::new(header.clone()),
+			justification: justification.clone(),
+		};
+		let indirect_submit_finality_proof_call =
+			BridgeGrandpaCall::<TestHeader>::submit_finality_proof(Box::new(header), justification);
+		assert_eq!(
+			direct_submit_finality_proof_call.encode(),
+			indirect_submit_finality_proof_call.encode()
+		);
+	}
+
 	generate_owned_bridge_module_tests!(BasicOperatingMode::Normal, BasicOperatingMode::Halted);
 }