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/modules/xcm-bridge-hub-router/src/mock.rs

@@ -49,9 +49,9 @@ construct_runtime! {
 parameter_types! {
 	pub ThisNetworkId: NetworkId = Polkadot;
 	pub BridgedNetworkId: NetworkId = Kusama;
-	pub UniversalLocation: InteriorMultiLocation = X2(GlobalConsensus(ThisNetworkId::get()), Parachain(1000));
-	pub SiblingBridgeHubLocation: MultiLocation = ParentThen(X1(Parachain(1002))).into();
-	pub BridgeFeeAsset: AssetId = MultiLocation::parent().into();
+	pub UniversalLocation: InteriorLocation = [GlobalConsensus(ThisNetworkId::get()), Parachain(1000)].into();
+	pub SiblingBridgeHubLocation: Location = ParentThen([Parachain(1002)].into()).into();
+	pub BridgeFeeAsset: AssetId = Location::parent().into();
 	pub BridgeTable: Vec<NetworkExportTableItem>
 		= vec![
 			NetworkExportTableItem::new(
@@ -61,7 +61,7 @@ parameter_types! {
 				Some((BridgeFeeAsset::get(), BASE_FEE).into())
 			)
 		];
-	pub UnknownXcmVersionLocation: MultiLocation = MultiLocation::new(2, X2(GlobalConsensus(BridgedNetworkId::get()), Parachain(9999)));
+	pub UnknownXcmVersionLocation: Location = Location::new(2, [GlobalConsensus(BridgedNetworkId::get()), Parachain(9999)]);
 }
 
 #[derive_impl(frame_system::config_preludes::TestDefaultConfig as frame_system::DefaultConfig)]
@@ -87,11 +87,11 @@ impl pallet_xcm_bridge_hub_router::Config<()> for TestRuntime {
 }
 
 pub struct LatestOrNoneForLocationVersionChecker<Location>(sp_std::marker::PhantomData<Location>);
-impl<Location: Contains<MultiLocation>> GetVersion
-	for LatestOrNoneForLocationVersionChecker<Location>
+impl<LocationValue: Contains<Location>> GetVersion
+	for LatestOrNoneForLocationVersionChecker<LocationValue>
 {
-	fn get_version_for(dest: &MultiLocation) -> Option<XcmVersion> {
-		if Location::contains(dest) {
+	fn get_version_for(dest: &Location) -> Option<XcmVersion> {
+		if LocationValue::contains(dest) {
 			return None
 		}
 		Some(XCM_VERSION)
@@ -110,7 +110,7 @@ impl SendXcm for TestToBridgeHubSender {
 	type Ticket = ();
 
 	fn validate(
-		_destination: &mut Option<MultiLocation>,
+		_destination: &mut Option<Location>,
 		_message: &mut Option<Xcm<()>>,
 	) -> SendResult<Self::Ticket> {
 		Ok(((), (BridgeFeeAsset::get(), HRMP_FEE).into()))