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/parachains/runtimes/bridge-hubs/test-utils/src/test_data/mod.rs

@@ -37,10 +37,10 @@ use xcm_executor::traits::{validate_export, ExportXcm};
 
 pub fn prepare_inbound_xcm<InnerXcmRuntimeCall>(
 	xcm_message: Xcm<InnerXcmRuntimeCall>,
-	destination: InteriorMultiLocation,
+	destination: InteriorLocation,
 ) -> Vec<u8> {
-	let location = xcm::VersionedInteriorMultiLocation::V3(destination);
-	let xcm = xcm::VersionedXcm::<InnerXcmRuntimeCall>::V3(xcm_message);
+	let location = xcm::VersionedInteriorLocation::V4(destination);
+	let xcm = xcm::VersionedXcm::<InnerXcmRuntimeCall>::V4(xcm_message);
 	// this is the `BridgeMessage` from polkadot xcm builder, but it has no constructor
 	// or public fields, so just tuple
 	// (double encoding, because `.encode()` is called on original Xcm BLOB when it is pushed
@@ -101,7 +101,7 @@ macro_rules! grab_haul_blob (
 /// which are transferred over bridge.
 pub(crate) fn simulate_message_exporter_on_bridged_chain<
 	SourceNetwork: Get<NetworkId>,
-	DestinationNetwork: Get<MultiLocation>,
+	DestinationNetwork: Get<Location>,
 	DestinationVersion: GetVersion,
 >(
 	(destination_network, destination_junctions): (NetworkId, Junctions),
@@ -109,8 +109,8 @@ pub(crate) fn simulate_message_exporter_on_bridged_chain<
 	grab_haul_blob!(GrabbingHaulBlob, GRABBED_HAUL_BLOB_PAYLOAD);
 
 	// lets pretend that some parachain on bridged chain exported the message
-	let universal_source_on_bridged_chain =
-		X2(GlobalConsensus(SourceNetwork::get()), Parachain(5678));
+	let universal_source_on_bridged_chain: Junctions =
+		[GlobalConsensus(SourceNetwork::get()), Parachain(5678)].into();
 	let channel = 1_u32;
 
 	// simulate XCM message export