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/pallets/xcmp-queue/src/mock.rs

@@ -124,8 +124,8 @@ impl cumulus_pallet_parachain_system::Config for Test {
 }
 
 parameter_types! {
-	pub const RelayChain: MultiLocation = MultiLocation::parent();
-	pub UniversalLocation: InteriorMultiLocation = X1(Parachain(1u32));
+	pub const RelayChain: Location = Location::parent();
+	pub UniversalLocation: InteriorLocation = [Parachain(1u32)].into();
 	pub UnitWeightCost: Weight = Weight::from_parts(1_000_000, 1024);
 	pub const MaxInstructions: u32 = 100;
 	pub const MaxAssetsIntoHolding: u32 = 64;
@@ -138,7 +138,7 @@ pub type LocalAssetTransactor = CurrencyAdapter<
 	Balances,
 	// Use this currency when it is a fungible asset matching the given location or name:
 	IsConcrete<RelayChain>,
-	// Do a simple punn to convert an AccountId32 MultiLocation into a native chain account ID:
+	// Do a simple punn to convert an AccountId32 Location into a native chain account ID:
 	LocationToAccountId,
 	// Our chain's account ID type (we can't get away without mentioning it explicitly):
 	AccountId,
@@ -187,17 +187,14 @@ impl<RuntimeOrigin: OriginTrait> ConvertOrigin<RuntimeOrigin>
 	for SystemParachainAsSuperuser<RuntimeOrigin>
 {
 	fn convert_origin(
-		origin: impl Into<MultiLocation>,
+		origin: impl Into<Location>,
 		kind: OriginKind,
-	) -> Result<RuntimeOrigin, MultiLocation> {
+	) -> Result<RuntimeOrigin, Location> {
 		let origin = origin.into();
 		if kind == OriginKind::Superuser &&
 			matches!(
-				origin,
-				MultiLocation {
-					parents: 1,
-					interior: X1(Parachain(id)),
-				} if ParaId::from(id).is_system(),
+				origin.unpack(),
+				(1,	[Parachain(id)]) if ParaId::from(*id).is_system(),
 			) {
 			Ok(RuntimeOrigin::root())
 		} else {
@@ -256,7 +253,7 @@ impl<T: OnQueueChanged<ParaId>> EnqueueMessage<ParaId> for EnqueueToLocalStorage
 
 parameter_types! {
 	/// The asset ID for the asset that we use to pay for message delivery fees.
-	pub FeeAssetId: AssetId = Concrete(RelayChain::get());
+	pub FeeAssetId: AssetId = AssetId(RelayChain::get());
 	/// The base fee for the message delivery fees.
 	pub const BaseDeliveryFee: Balance = 300_000_000;
 	/// The fee per byte