[testnet] Allow governance to control fees for Rococo <> Westend bridge (#2139)

Right now governance could only control byte-fee component of Rococo <>
Westend message fees (paid at Asset Hubs). This PR changes it a bit:
1) governance now allowed to control both fee components - byte fee and
base fee;
2) base fee now includes cost of "default" delivery and confirmation
transactions, in addition to `ExportMessage` instruction cost.

bridges/bin/runtime-common/src/messages_generation.rs

@@ -16,10 +16,11 @@
 
 //! Helpers for generating message storage proofs, that are used by tests and by benchmarks.
 
-use crate::messages::{BridgedChain, HashOf, HasherOf, MessageBridge};
+use crate::messages::{AccountIdOf, BridgedChain, HashOf, HasherOf, MessageBridge, ThisChain};
 
 use bp_messages::{
-	storage_keys, LaneId, MessageKey, MessageNonce, MessagePayload, OutboundLaneData,
+	storage_keys, InboundLaneData, LaneId, MessageKey, MessageNonce, MessagePayload,
+	OutboundLaneData,
 };
 use bp_runtime::{record_all_trie_keys, RawStorageProof, StorageProofSize};
 use codec::Encode;
@@ -104,6 +105,38 @@ where
 	(root, storage_proof)
 }
 
+/// Prepare storage proof of given messages delivery.
+///
+/// Returns state trie root and nodes with prepared messages.
+pub fn prepare_message_delivery_storage_proof<B>(
+	lane: LaneId,
+	inbound_lane_data: InboundLaneData<AccountIdOf<ThisChain<B>>>,
+	size: StorageProofSize,
+) -> (HashOf<BridgedChain<B>>, RawStorageProof)
+where
+	B: MessageBridge,
+{
+	// prepare Bridged chain storage with inbound lane state
+	let storage_key = storage_keys::inbound_lane_data_key(B::BRIDGED_MESSAGES_PALLET_NAME, &lane).0;
+	let mut root = Default::default();
+	let mut mdb = MemoryDB::default();
+	{
+		let mut trie =
+			TrieDBMutBuilderV1::<HasherOf<BridgedChain<B>>>::new(&mut mdb, &mut root).build();
+		let inbound_lane_data = grow_trie_leaf_value(inbound_lane_data.encode(), size);
+		trie.insert(&storage_key, &inbound_lane_data)
+			.map_err(|_| "TrieMut::insert has failed")
+			.expect("TrieMut::insert should not fail in benchmarks");
+	}
+
+	// generate storage proof to be delivered to This chain
+	let storage_proof = record_all_trie_keys::<LayoutV1<HasherOf<BridgedChain<B>>>, _>(&mdb, &root)
+		.map_err(|_| "record_all_trie_keys has failed")
+		.expect("record_all_trie_keys should not fail in benchmarks");
+
+	(root, storage_proof)
+}
+
 /// Add extra data to the trie leaf value so that it'll be of given size.
 pub fn grow_trie_leaf_value(mut value: Vec<u8>, size: StorageProofSize) -> Vec<u8> {
 	match size {