XCMv4 (#1230)

# Note for reviewer

Most changes are just syntax changes necessary for the new version.
Most important files should be the ones under the `xcm` folder.

# Description 

Added XCMv4.

## Removed `Multi` prefix
The following types have been renamed:
- MultiLocation -> Location
- MultiAsset -> Asset
- MultiAssets -> Assets
- InteriorMultiLocation -> InteriorLocation
- MultiAssetFilter -> AssetFilter
- VersionedMultiAsset -> VersionedAsset
- WildMultiAsset -> WildAsset
- VersionedMultiLocation -> VersionedLocation

In order to fix a name conflict, the `Assets` in `xcm-executor` were
renamed to `HoldingAssets`, as they represent assets in holding.

## Removed `Abstract` asset id

It was not being used anywhere and this simplifies the code.

Now assets are just constructed as follows:

```rust
let asset: Asset = (AssetId(Location::new(1, Here)), 100u128).into();
```

No need for specifying `Concrete` anymore.

## Outcome is now a named fields struct

Instead of

```rust
pub enum Outcome {
  Complete(Weight),
  Incomplete(Weight, Error),
  Error(Error),
}
```

we now have

```rust
pub enum Outcome {
  Complete { used: Weight },
  Incomplete { used: Weight, error: Error },
  Error { error: Error },
}
```

## Added Reanchorable trait

Now both locations and assets implement this trait, making it easier to
reanchor both.

## New syntax for building locations and junctions

Now junctions are built using the following methods:

```rust
let location = Location {
    parents: 1,
    interior: [Parachain(1000), PalletInstance(50), GeneralIndex(1984)].into()
};
```

or

```rust
let location = Location::new(1, [Parachain(1000), PalletInstance(50), GeneralIndex(1984)]);
```

And they are matched like so:

```rust
match location.unpack() {
  (1, [Parachain(id)]) => ...
  (0, Here) => ...,
  (1, [_]) => ...,
}
```

This syntax is mandatory in v4, and has been also implemented for v2 and
v3 for easier migration.

This was needed to make all sizes smaller.

# TODO
- [x] Scaffold v4
- [x] Port github.com/paritytech/polkadot/pull/7236
- [x] Remove `Multi` prefix
- [x] Remove `Abstract` asset id

---------

Co-authored-by: command-bot <>
Co-authored-by: Keith Yeung <kungfukeith11@gmail.com>

cumulus/parachains/runtimes/bridge-hubs/bridge-hub-westend/src/lib.rs

@@ -352,7 +352,7 @@ impl cumulus_pallet_aura_ext::Config for Runtime {}
 
 parameter_types! {
 	/// The asset ID for the asset that we use to pay for message delivery fees.
-	pub FeeAssetId: AssetId = Concrete(xcm_config::WestendLocation::get());
+	pub FeeAssetId: AssetId = AssetId(xcm_config::WestendLocation::get());
 	/// The base fee for the message delivery fees.
 	pub const BaseDeliveryFee: u128 = CENTS.saturating_mul(3);
 }
@@ -797,28 +797,28 @@ impl_runtime_apis! {
 
 			use pallet_xcm::benchmarking::Pallet as PalletXcmExtrinsicsBenchmark;
 			impl pallet_xcm::benchmarking::Config for Runtime {
-				fn reachable_dest() -> Option<MultiLocation> {
+				fn reachable_dest() -> Option<Location> {
 					Some(Parent.into())
 				}
 
-				fn teleportable_asset_and_dest() -> Option<(MultiAsset, MultiLocation)> {
+				fn teleportable_asset_and_dest() -> Option<(Asset, Location)> {
 					// Relay/native token can be teleported between BH and Relay.
 					Some((
-						MultiAsset {
+						Asset {
 							fun: Fungible(EXISTENTIAL_DEPOSIT),
-							id: Concrete(Parent.into())
+							id: AssetId(Parent.into())
 						},
 						Parent.into(),
 					))
 				}
 
-				fn reserve_transferable_asset_and_dest() -> Option<(MultiAsset, MultiLocation)> {
+				fn reserve_transferable_asset_and_dest() -> Option<(Asset, Location)> {
 					// Reserve transfers are disabled on BH.
 					None
 				}
 
 				fn set_up_complex_asset_transfer(
-				) -> Option<(MultiAssets, u32, MultiLocation, Box<dyn FnOnce()>)> {
+				) -> Option<(Assets, u32, Location, Box<dyn FnOnce()>)> {
 					// BH only supports teleports to system parachain.
 					// Relay/native token can be teleported between BH and Relay.
 					let native_location = Parent.into();
@@ -834,7 +834,7 @@ impl_runtime_apis! {
 			use xcm_config::WestendLocation;
 
 			parameter_types! {
-				pub ExistentialDepositMultiAsset: Option<MultiAsset> = Some((
+				pub ExistentialDepositAsset: Option<Asset> = Some((
 					WestendLocation::get(),
 					ExistentialDeposit::get()
 				).into());
@@ -845,17 +845,17 @@ impl_runtime_apis! {
 				type AccountIdConverter = xcm_config::LocationToAccountId;
 				type DeliveryHelper = cumulus_primitives_utility::ToParentDeliveryHelper<
 					xcm_config::XcmConfig,
-					ExistentialDepositMultiAsset,
+					ExistentialDepositAsset,
 					xcm_config::PriceForParentDelivery,
 				>;
-				fn valid_destination() -> Result<MultiLocation, BenchmarkError> {
+				fn valid_destination() -> Result<Location, BenchmarkError> {
 					Ok(WestendLocation::get())
 				}
-				fn worst_case_holding(_depositable_count: u32) -> MultiAssets {
-					// just concrete assets according to relay chain.
-					let assets: Vec<MultiAsset> = vec![
-						MultiAsset {
-							id: Concrete(WestendLocation::get()),
+				fn worst_case_holding(_depositable_count: u32) -> Assets {
+					// just assets according to relay chain.
+					let assets: Vec<Asset> = vec![
+						Asset {
+							id: AssetId(WestendLocation::get()),
 							fun: Fungible(1_000_000 * UNITS),
 						}
 					];
@@ -864,12 +864,12 @@ impl_runtime_apis! {
 			}
 
 			parameter_types! {
-				pub const TrustedTeleporter: Option<(MultiLocation, MultiAsset)> = Some((
+				pub const TrustedTeleporter: Option<(Location, Asset)> = Some((
 					WestendLocation::get(),
-					MultiAsset { fun: Fungible(UNITS), id: Concrete(WestendLocation::get()) },
+					Asset { fun: Fungible(UNITS), id: AssetId(WestendLocation::get()) },
 				));
 				pub const CheckedAccount: Option<(AccountId, xcm_builder::MintLocation)> = None;
-				pub const TrustedReserve: Option<(MultiLocation, MultiAsset)> = None;
+				pub const TrustedReserve: Option<(Location, Asset)> = None;
 			}
 
 			impl pallet_xcm_benchmarks::fungible::Config for Runtime {
@@ -879,9 +879,9 @@ impl_runtime_apis! {
 				type TrustedTeleporter = TrustedTeleporter;
 				type TrustedReserve = TrustedReserve;
 
-				fn get_multi_asset() -> MultiAsset {
-					MultiAsset {
-						id: Concrete(WestendLocation::get()),
+				fn get_asset() -> Asset {
+					Asset {
+						id: AssetId(WestendLocation::get()),
 						fun: Fungible(UNITS),
 					}
 				}
@@ -895,35 +895,35 @@ impl_runtime_apis! {
 					(0u64, Response::Version(Default::default()))
 				}
 
-				fn worst_case_asset_exchange() -> Result<(MultiAssets, MultiAssets), BenchmarkError> {
+				fn worst_case_asset_exchange() -> Result<(Assets, Assets), BenchmarkError> {
 					Err(BenchmarkError::Skip)
 				}
 
-				fn universal_alias() -> Result<(MultiLocation, Junction), BenchmarkError> {
+				fn universal_alias() -> Result<(Location, Junction), BenchmarkError> {
 					Err(BenchmarkError::Skip)
 				}
 
-				fn transact_origin_and_runtime_call() -> Result<(MultiLocation, RuntimeCall), BenchmarkError> {
+				fn transact_origin_and_runtime_call() -> Result<(Location, RuntimeCall), BenchmarkError> {
 					Ok((WestendLocation::get(), frame_system::Call::remark_with_event { remark: vec![] }.into()))
 				}
 
-				fn subscribe_origin() -> Result<MultiLocation, BenchmarkError> {
+				fn subscribe_origin() -> Result<Location, BenchmarkError> {
 					Ok(WestendLocation::get())
 				}
 
-				fn claimable_asset() -> Result<(MultiLocation, MultiLocation, MultiAssets), BenchmarkError> {
+				fn claimable_asset() -> Result<(Location, Location, Assets), BenchmarkError> {
 					let origin = WestendLocation::get();
-					let assets: MultiAssets = (Concrete(WestendLocation::get()), 1_000 * UNITS).into();
-					let ticket = MultiLocation { parents: 0, interior: Here };
+					let assets: Assets = (AssetId(WestendLocation::get()), 1_000 * UNITS).into();
+					let ticket = Location { parents: 0, interior: Here };
 					Ok((origin, ticket, assets))
 				}
 
-				fn unlockable_asset() -> Result<(MultiLocation, MultiLocation, MultiAsset), BenchmarkError> {
+				fn unlockable_asset() -> Result<(Location, Location, Asset), BenchmarkError> {
 					Err(BenchmarkError::Skip)
 				}
 
 				fn export_message_origin_and_destination(
-				) -> Result<(MultiLocation, NetworkId, InteriorMultiLocation), BenchmarkError> {
+				) -> Result<(Location, NetworkId, InteriorLocation), BenchmarkError> {
 					// save XCM version for remote bridge hub
 					let _ = PolkadotXcm::force_xcm_version(
 						RuntimeOrigin::root(),
@@ -943,12 +943,12 @@ impl_runtime_apis! {
 						(
 							bridge_to_rococo_config::FromAssetHubWestendToAssetHubRococoRoute::get().location,
 							NetworkId::Rococo,
-							X1(Parachain(bridge_to_rococo_config::AssetHubRococoParaId::get().into()))
+							[Parachain(bridge_to_rococo_config::AssetHubRococoParaId::get().into())].into()
 						)
 					)
 				}
 
-				fn alias_origin() -> Result<(MultiLocation, MultiLocation), BenchmarkError> {
+				fn alias_origin() -> Result<(Location, Location), BenchmarkError> {
 					Err(BenchmarkError::Skip)
 				}
 			}
@@ -995,7 +995,7 @@ impl_runtime_apis! {
 						Runtime,
 						bridge_to_rococo_config::BridgeGrandpaRococoInstance,
 						bridge_to_rococo_config::WithBridgeHubRococoMessageBridge,
-					>(params, generate_xcm_builder_bridge_message_sample(X2(GlobalConsensus(Westend), Parachain(42))))
+					>(params, generate_xcm_builder_bridge_message_sample([GlobalConsensus(Westend), Parachain(42)].into()))
 				}
 
 				fn prepare_message_delivery_proof(