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>

substrate/frame/contracts/mock-network/src/tests.rs

@@ -31,7 +31,7 @@ use frame_support::{
 use pallet_balances::{BalanceLock, Reasons};
 use pallet_contracts::{Code, CollectEvents, DebugInfo, Determinism};
 use pallet_contracts_fixtures::compile_module;
-use xcm::{v3::prelude::*, VersionedMultiLocation, VersionedXcm};
+use xcm::{v4::prelude::*, VersionedLocation, VersionedXcm};
 use xcm_simulator::TestExt;
 
 type ParachainContracts = pallet_contracts::Pallet<parachain::Runtime>;
@@ -82,7 +82,7 @@ fn test_xcm_execute() {
 		let amount: u128 = 10 * CENTS;
 
 		// The XCM used to transfer funds to Bob.
-		let message: xcm_simulator::Xcm<()> = Xcm(vec![
+		let message: Xcm<()> = Xcm(vec![
 			WithdrawAsset(vec![(Here, amount).into()].into()),
 			DepositAsset {
 				assets: All.into(),
@@ -96,7 +96,7 @@ fn test_xcm_execute() {
 			0,
 			Weight::MAX,
 			None,
-			VersionedXcm::V3(message).encode(),
+			VersionedXcm::V4(message).encode(),
 			DebugInfo::UnsafeDebug,
 			CollectEvents::UnsafeCollect,
 			Determinism::Enforced,
@@ -106,7 +106,7 @@ fn test_xcm_execute() {
 
 		let mut data = &result.data[..];
 		let outcome = Outcome::decode(&mut data).expect("Failed to decode xcm_execute Outcome");
-		assert_matches!(outcome, Outcome::Complete(_));
+		assert_matches!(outcome, Outcome::Complete { .. });
 
 		// Check if the funds are subtracted from the account of Alice and added to the account of
 		// Bob.
@@ -137,7 +137,7 @@ fn test_xcm_execute_filtered_call() {
 			0,
 			Weight::MAX,
 			None,
-			VersionedXcm::V3(message).encode(),
+			VersionedXcm::V4(message).encode(),
 			DebugInfo::UnsafeDebug,
 			CollectEvents::UnsafeCollect,
 			Determinism::Enforced,
@@ -178,7 +178,7 @@ fn test_xcm_execute_reentrant_call() {
 			0,
 			Weight::MAX,
 			None,
-			VersionedXcm::V3(message).encode(),
+			VersionedXcm::V4(message).encode(),
 			DebugInfo::UnsafeDebug,
 			CollectEvents::UnsafeCollect,
 			Determinism::Enforced,
@@ -188,7 +188,10 @@ fn test_xcm_execute_reentrant_call() {
 
 		let mut data = &result.data[..];
 		let outcome = Outcome::decode(&mut data).expect("Failed to decode xcm_execute Outcome");
-		assert_matches!(outcome, Outcome::Incomplete(_, XcmError::ExpectationFalse));
+		assert_matches!(
+			outcome,
+			Outcome::Incomplete { used: _, error: XcmError::ExpectationFalse }
+		);
 
 		// Funds should not change hands as the XCM transact failed.
 		assert_eq!(ParachainBalances::free_balance(BOB), INITIAL_BALANCE);
@@ -203,15 +206,15 @@ fn test_xcm_send() {
 
 	// Send XCM instructions through the contract, to lock some funds on the relay chain.
 	ParaA::execute_with(|| {
-		let dest = MultiLocation::from(Parent);
-		let dest = VersionedMultiLocation::V3(dest);
+		let dest = Location::from(Parent);
+		let dest = VersionedLocation::V4(dest);
 
-		let message: xcm_simulator::Xcm<()> = Xcm(vec![
+		let message: Xcm<()> = Xcm(vec![
 			WithdrawAsset((Here, fee).into()),
 			BuyExecution { fees: (Here, fee).into(), weight_limit: WeightLimit::Unlimited },
 			LockAsset { asset: (Here, 5 * CENTS).into(), unlocker: (Parachain(1)).into() },
 		]);
-		let message = VersionedXcm::V3(message);
+		let message = VersionedXcm::V4(message);
 		let exec = ParachainContracts::bare_call(
 			ALICE,
 			contract_addr.clone(),