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>

bridges/snowbridge/parachain/runtime/runtime-common/src/lib.rs

@@ -46,43 +46,38 @@ impl<Balance, AccountId, FeeAssetLocation, EthereumNetwork, AssetTransactor, Fee
 	> where
 	Balance: BaseArithmetic + Unsigned + Copy + From<u128> + Into<u128>,
 	AccountId: Clone + Into<[u8; 32]> + From<[u8; 32]>,
-	FeeAssetLocation: Get<MultiLocation>,
+	FeeAssetLocation: Get<Location>,
 	EthereumNetwork: Get<NetworkId>,
 	AssetTransactor: TransactAsset,
 	FeeProvider: SendMessageFeeProvider<Balance = Balance>,
 {
-	fn handle_fee(
-		fees: MultiAssets,
-		context: Option<&XcmContext>,
-		reason: FeeReason,
-	) -> MultiAssets {
+	fn handle_fee(fees: Assets, context: Option<&XcmContext>, reason: FeeReason) -> Assets {
 		let token_location = FeeAssetLocation::get();
 
 		// Check the reason to see if this export is for snowbridge.
 		if !matches!(
 			reason,
-			FeeReason::Export { network: bridged_network, destination }
-				if bridged_network == EthereumNetwork::get() && destination == Here
+			FeeReason::Export { network: bridged_network, ref destination }
+				if bridged_network == EthereumNetwork::get() && destination == &Here
 		) {
 			return fees
 		}
 
 		// Get the parachain sovereign from the `context`.
-		let para_sovereign = if let Some(XcmContext {
-			origin: Some(MultiLocation { parents: 1, interior }),
-			..
-		}) = context
-		{
-			if let Some(Parachain(sibling_para_id)) = interior.first() {
-				let account: AccountId =
-					sibling_sovereign_account_raw((*sibling_para_id).into()).into();
-				account
+		let para_sovereign =
+			if let Some(XcmContext { origin: Some(Location { parents: 1, interior }), .. }) =
+				context
+			{
+				if let Some(Parachain(sibling_para_id)) = interior.first() {
+					let account: AccountId =
+						sibling_sovereign_account_raw((*sibling_para_id).into()).into();
+					account
+				} else {
+					return fees
+				}
 			} else {
 				return fees
-			}
-		} else {
-			return fees
-		};
+			};
 
 		// Get the total fee offered by export message.
 		let maybe_total_supplied_fee: Option<(usize, Balance)> = fees
@@ -90,8 +85,8 @@ impl<Balance, AccountId, FeeAssetLocation, EthereumNetwork, AssetTransactor, Fee
 			.iter()
 			.enumerate()
 			.filter_map(|(index, asset)| {
-				if let MultiAsset { id: Concrete(location), fun: Fungible(amount) } = asset {
-					if *location == token_location {
+				if let Asset { id: location, fun: Fungible(amount) } = asset {
+					if location.0 == token_location {
 						return Some((index, (*amount).into()))
 					}
 				}
@@ -104,7 +99,7 @@ impl<Balance, AccountId, FeeAssetLocation, EthereumNetwork, AssetTransactor, Fee
 			if remote_fee > (0u128).into() {
 				// Refund remote component of fee to physical origin
 				deposit_or_burn_fee::<AssetTransactor, _>(
-					MultiAsset { id: Concrete(token_location), fun: Fungible(remote_fee.into()) }
+					Asset { id: AssetId(token_location.clone()), fun: Fungible(remote_fee.into()) }
 						.into(),
 					context,
 					para_sovereign,
@@ -112,8 +107,8 @@ impl<Balance, AccountId, FeeAssetLocation, EthereumNetwork, AssetTransactor, Fee
 				// Return remaining fee to the next fee handler in the chain.
 				let mut modified_fees = fees.inner().clone();
 				modified_fees.remove(fee_index);
-				modified_fees.push(MultiAsset {
-					id: Concrete(token_location),
+				modified_fees.push(Asset {
+					id: AssetId(token_location),
 					fun: Fungible((total_fee - remote_fee).into()),
 				});
 				return modified_fees.into()