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>

polkadot/runtime/rococo/src/impls.rs

@@ -22,7 +22,7 @@ use primitives::Balance;
 use rococo_runtime_constants::currency::*;
 use runtime_common::identity_migrator::{OnReapIdentity, WeightInfo};
 use sp_std::{marker::PhantomData, prelude::*};
-use xcm::{latest::prelude::*, VersionedMultiLocation, VersionedXcm};
+use xcm::{latest::prelude::*, VersionedLocation, VersionedXcm};
 use xcm_executor::traits::TransactAsset;
 
 /// A type containing the encoding of the People Chain pallets in its runtime. Used to construct any
@@ -95,9 +95,9 @@ where
 		let total_to_send = Self::calculate_remote_deposit(fields, subs);
 
 		// define asset / destination from relay perspective
-		let roc = MultiAsset { id: Concrete(Here.into_location()), fun: Fungible(total_to_send) };
+		let roc = Asset { id: AssetId(Here.into_location()), fun: Fungible(total_to_send) };
 		// People Chain: ParaId 1004
-		let destination: MultiLocation = MultiLocation::new(0, Parachain(1004));
+		let destination: Location = Location::new(0, Parachain(1004));
 
 		// Do `check_out` accounting since the XCM Executor's `InitiateTeleport` doesn't support
 		// unpaid teleports.
@@ -138,11 +138,9 @@ where
 		);
 
 		// reanchor
-		let roc_reanchored: MultiAssets = vec![MultiAsset {
-			id: Concrete(MultiLocation::new(1, Here)),
-			fun: Fungible(total_to_send),
-		}]
-		.into();
+		let roc_reanchored: Assets =
+			vec![Asset { id: AssetId(Location::new(1, Here)), fun: Fungible(total_to_send) }]
+				.into();
 
 		let poke = PeopleRuntimePallets::<AccountId>::IdentityMigrator(PokeDeposit(who.clone()));
 		let remote_weight_limit = MigratorWeights::<Runtime>::poke_deposit().saturating_mul(2);
@@ -172,8 +170,8 @@ where
 		// send
 		let _ = <pallet_xcm::Pallet<Runtime>>::send(
 			RawOrigin::Root.into(),
-			Box::new(VersionedMultiLocation::V3(destination)),
-			Box::new(VersionedXcm::V3(program)),
+			Box::new(VersionedLocation::V4(destination)),
+			Box::new(VersionedXcm::V4(program)),
 		)?;
 		Ok(())
 	}