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/xcm/xcm-builder/src/matches_location.rs

@@ -14,37 +14,47 @@
 // You should have received a copy of the GNU General Public License
 // along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
 
-//! Various implementations and utilities for matching and filtering `MultiLocation` and
-//! `InteriorMultiLocation` types.
+//! Various implementations and utilities for matching and filtering `Location` and
+//! `InteriorLocation` types.
 
 use frame_support::traits::{Contains, Get};
-use xcm::latest::{InteriorMultiLocation, MultiLocation, NetworkId};
+use xcm::latest::{InteriorLocation, Location, NetworkId};
 
-/// An implementation of `Contains` that checks for `MultiLocation` or
-/// `InteriorMultiLocation` if starts with the provided type `T`.
-pub struct StartsWith<T>(sp_std::marker::PhantomData<T>);
-impl<T: Get<MultiLocation>> Contains<MultiLocation> for StartsWith<T> {
-	fn contains(t: &MultiLocation) -> bool {
-		t.starts_with(&T::get())
+/// An implementation of `Contains` that checks for `Location` or
+/// `InteriorLocation` if starts with the provided type `T`.
+pub struct StartsWith<T, L = Location>(sp_std::marker::PhantomData<(T, L)>);
+impl<T: Get<L>, L: TryInto<Location> + Clone> Contains<L> for StartsWith<T, L> {
+	fn contains(location: &L) -> bool {
+		let latest_location: Location = if let Ok(location) = (*location).clone().try_into() {
+			location
+		} else {
+			return false;
+		};
+		let latest_t = if let Ok(location) = T::get().try_into() {
+			location
+		} else {
+			return false;
+		};
+		latest_location.starts_with(&latest_t)
 	}
 }
-impl<T: Get<InteriorMultiLocation>> Contains<InteriorMultiLocation> for StartsWith<T> {
-	fn contains(t: &InteriorMultiLocation) -> bool {
+impl<T: Get<InteriorLocation>> Contains<InteriorLocation> for StartsWith<T> {
+	fn contains(t: &InteriorLocation) -> bool {
 		t.starts_with(&T::get())
 	}
 }
 
-/// An implementation of `Contains` that checks for `MultiLocation` or
-/// `InteriorMultiLocation` if starts with expected `GlobalConsensus(NetworkId)` provided as type
+/// An implementation of `Contains` that checks for `Location` or
+/// `InteriorLocation` if starts with expected `GlobalConsensus(NetworkId)` provided as type
 /// `T`.
 pub struct StartsWithExplicitGlobalConsensus<T>(sp_std::marker::PhantomData<T>);
-impl<T: Get<NetworkId>> Contains<MultiLocation> for StartsWithExplicitGlobalConsensus<T> {
-	fn contains(location: &MultiLocation) -> bool {
-		matches!(location.interior.global_consensus(), Ok(requested_network) if requested_network.eq(&T::get()))
+impl<T: Get<NetworkId>> Contains<Location> for StartsWithExplicitGlobalConsensus<T> {
+	fn contains(location: &Location) -> bool {
+		matches!(location.interior().global_consensus(), Ok(requested_network) if requested_network.eq(&T::get()))
 	}
 }
-impl<T: Get<NetworkId>> Contains<InteriorMultiLocation> for StartsWithExplicitGlobalConsensus<T> {
-	fn contains(location: &InteriorMultiLocation) -> bool {
+impl<T: Get<NetworkId>> Contains<InteriorLocation> for StartsWithExplicitGlobalConsensus<T> {
+	fn contains(location: &InteriorLocation) -> bool {
 		matches!(location.global_consensus(), Ok(requested_network) if requested_network.eq(&T::get()))
 	}
 }