Add test cases to Cumulus which simulates real e2e message delivery

[bkontur]

Pseudocode:

fn bridge_hub_rococo_dispatch_works() {
	<initialize-externalities>::execute_with(|| {	
		let bridge_message = BridgeMessage {
			universal_dest: V3(X2(GlobalConsensus(...), Parachain(1234))),
			xcm: Xcm(...)
		};

		assert_ok!(pallet_bridge_grandpa::Pallet::<Runtime, BridgeGrandpaWococoInstance>::submit_finality_proof(...));
		assert_ok!(pallet_bridge_parachains::Pallet::<Runtime, BridgeParachainWococoInstance>::submit_parachain_heads(...));
		assert_ok!(pallet_bridge_messages::Pallet::<Runtime, WithBridgeHubWococoMessagesInstance>::receive_messages_proof(..., bridge_message, ...));
		
		// get message from `XcmpQueue::take_outbound_messages` for 1234
		let dispatched_xcm = RuntimeHelper::<HrmpChannelSource>::take_xcm(1234);
		asset_eq!(xcm, dispatched_xcm);
	})
}

• I will prepare everything around, but will need help with submit_finality_proof/submit_parachain_heads/receive_messages_proof proofs (lots of this helper code is in benchmarking stuff e.g.: prepare_messages_storage_proof ...)
• add test for DeliveryConfirmationPayments when receive_messages_delivery_proof
• check economics in tests (hit delivery rewards constants)

  pub storage DeliveryRewardInBalance: u64 = 1_000_000;
  pub storage RequiredStakeForStakeAndSlash: Balance = 1_000_000;
  

[acatangiu]

AFAICT, receive_single_message_proof_with_dispatch benchmark implements and verifies this e2e message delivery:

• starts with messages 1..=20 already delivered
• opens HRMP channel to para 42
• sets expected message destination to X2(GlobalConsensus(<parent-relay>), Parachain(42))
• prepares inbound xcm message (consisting of multiple ClearOrigin instructions),
• builds FromBridgedChainMessagesProof containing message above with nonce 21
• calls receive_messages_proof() with above proof as if submitted by relayer
• verifies InboundLanes::<bla>::last_delivered_nonce() == 21
• verifies XcmpQueue::outbound_messages has new xcm message (dispatch successful)

It doesn't explicitly verify that the final XcmpQueue::take_outbound_messages() equals the original xcm payload (vec![ClearOrigin; n]), but we can enhance it to do that too as a nice to have.

[acatangiu]

But above only verifies incoming (over bridge) message (xcm) dispatch, not complete flow. We want a runtime test that fully verifies side-effects of a relayer submitting batch(grandpa_finality, parachain_heads, message_proof), including relayer slash/reward.