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/primitives/router/src/inbound/tests.rs

@@ -2,7 +2,7 @@ use super::GlobalConsensusEthereumConvertsFor;
 use crate::inbound::CallIndex;
 use frame_support::parameter_types;
 use hex_literal::hex;
-use xcm::v3::prelude::*;
+use xcm::v4::prelude::*;
 use xcm_executor::traits::ConvertLocation;
 
 const NETWORK: NetworkId = Ethereum { chain_id: 11155111 };
@@ -20,7 +20,7 @@ parameter_types! {
 fn test_contract_location_with_network_converts_successfully() {
 	let expected_account: [u8; 32] =
 		hex!("ce796ae65569a670d0c1cc1ac12515a3ce21b5fbf729d63d7b289baad070139d");
-	let contract_location = MultiLocation { parents: 2, interior: X1(GlobalConsensus(NETWORK)) };
+	let contract_location = Location::new(2, [GlobalConsensus(NETWORK)]);
 
 	let account =
 		GlobalConsensusEthereumConvertsFor::<[u8; 32]>::convert_location(&contract_location)
@@ -31,8 +31,7 @@ fn test_contract_location_with_network_converts_successfully() {
 
 #[test]
 fn test_contract_location_with_incorrect_location_fails_convert() {
-	let contract_location =
-		MultiLocation { parents: 2, interior: X2(GlobalConsensus(Polkadot), Parachain(1000)) };
+	let contract_location = Location::new(2, [GlobalConsensus(Polkadot), Parachain(1000)]);
 
 	assert_eq!(
 		GlobalConsensusEthereumConvertsFor::<[u8; 32]>::convert_location(&contract_location),