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/fungible_adapter.rs

@@ -25,7 +25,10 @@ use frame_support::traits::{
 };
 use sp_std::{marker::PhantomData, prelude::*, result};
 use xcm::latest::prelude::*;
-use xcm_executor::traits::{ConvertLocation, Error as MatchError, MatchesFungible, TransactAsset};
+use xcm_executor::{
+	traits::{ConvertLocation, Error as MatchError, MatchesFungible, TransactAsset},
+	AssetsInHolding,
+};
 
 /// [`TransactAsset`] implementation that allows the use of a [`fungible`] implementation for
 /// handling an asset in the XCM executor.
@@ -41,11 +44,11 @@ impl<
 	> TransactAsset for FungibleTransferAdapter<Fungible, Matcher, AccountIdConverter, AccountId>
 {
 	fn internal_transfer_asset(
-		what: &MultiAsset,
-		from: &MultiLocation,
-		to: &MultiLocation,
+		what: &Asset,
+		from: &Location,
+		to: &Location,
 		_context: &XcmContext,
-	) -> result::Result<xcm_executor::Assets, XcmError> {
+	) -> result::Result<AssetsInHolding, XcmError> {
 		log::trace!(
 			target: "xcm::fungible_adapter",
 			"internal_transfer_asset what: {:?}, from: {:?}, to: {:?}",
@@ -111,11 +114,7 @@ impl<
 	> TransactAsset
 	for FungibleMutateAdapter<Fungible, Matcher, AccountIdConverter, AccountId, CheckingAccount>
 {
-	fn can_check_in(
-		_origin: &MultiLocation,
-		what: &MultiAsset,
-		_context: &XcmContext,
-	) -> XcmResult {
+	fn can_check_in(_origin: &Location, what: &Asset, _context: &XcmContext) -> XcmResult {
 		log::trace!(
 			target: "xcm::fungible_adapter",
 			"can_check_in origin: {:?}, what: {:?}",
@@ -132,7 +131,7 @@ impl<
 		}
 	}
 
-	fn check_in(_origin: &MultiLocation, what: &MultiAsset, _context: &XcmContext) {
+	fn check_in(_origin: &Location, what: &Asset, _context: &XcmContext) {
 		log::trace!(
 			target: "xcm::fungible_adapter",
 			"check_in origin: {:?}, what: {:?}",
@@ -149,7 +148,7 @@ impl<
 		}
 	}
 
-	fn can_check_out(_dest: &MultiLocation, what: &MultiAsset, _context: &XcmContext) -> XcmResult {
+	fn can_check_out(_dest: &Location, what: &Asset, _context: &XcmContext) -> XcmResult {
 		log::trace!(
 			target: "xcm::fungible_adapter",
 			"check_out dest: {:?}, what: {:?}",
@@ -166,7 +165,7 @@ impl<
 		}
 	}
 
-	fn check_out(_dest: &MultiLocation, what: &MultiAsset, _context: &XcmContext) {
+	fn check_out(_dest: &Location, what: &Asset, _context: &XcmContext) {
 		log::trace!(
 			target: "xcm::fungible_adapter",
 			"check_out dest: {:?}, what: {:?}",
@@ -184,11 +183,7 @@ impl<
 		}
 	}
 
-	fn deposit_asset(
-		what: &MultiAsset,
-		who: &MultiLocation,
-		_context: Option<&XcmContext>,
-	) -> XcmResult {
+	fn deposit_asset(what: &Asset, who: &Location, _context: Option<&XcmContext>) -> XcmResult {
 		log::trace!(
 			target: "xcm::fungible_adapter",
 			"deposit_asset what: {:?}, who: {:?}",
@@ -203,10 +198,10 @@ impl<
 	}
 
 	fn withdraw_asset(
-		what: &MultiAsset,
-		who: &MultiLocation,
+		what: &Asset,
+		who: &Location,
 		_context: Option<&XcmContext>,
-	) -> result::Result<xcm_executor::Assets, XcmError> {
+	) -> result::Result<AssetsInHolding, XcmError> {
 		log::trace!(
 			target: "xcm::fungible_adapter",
 			"deposit_asset what: {:?}, who: {:?}",
@@ -236,7 +231,7 @@ impl<
 	> TransactAsset
 	for FungibleAdapter<Fungible, Matcher, AccountIdConverter, AccountId, CheckingAccount>
 {
-	fn can_check_in(origin: &MultiLocation, what: &MultiAsset, context: &XcmContext) -> XcmResult {
+	fn can_check_in(origin: &Location, what: &Asset, context: &XcmContext) -> XcmResult {
 		FungibleMutateAdapter::<
 			Fungible,
 			Matcher,
@@ -246,7 +241,7 @@ impl<
 		>::can_check_in(origin, what, context)
 	}
 
-	fn check_in(origin: &MultiLocation, what: &MultiAsset, context: &XcmContext) {
+	fn check_in(origin: &Location, what: &Asset, context: &XcmContext) {
 		FungibleMutateAdapter::<
 			Fungible,
 			Matcher,
@@ -256,7 +251,7 @@ impl<
 		>::check_in(origin, what, context)
 	}
 
-	fn can_check_out(dest: &MultiLocation, what: &MultiAsset, context: &XcmContext) -> XcmResult {
+	fn can_check_out(dest: &Location, what: &Asset, context: &XcmContext) -> XcmResult {
 		FungibleMutateAdapter::<
 			Fungible,
 			Matcher,
@@ -266,7 +261,7 @@ impl<
 		>::can_check_out(dest, what, context)
 	}
 
-	fn check_out(dest: &MultiLocation, what: &MultiAsset, context: &XcmContext) {
+	fn check_out(dest: &Location, what: &Asset, context: &XcmContext) {
 		FungibleMutateAdapter::<
 			Fungible,
 			Matcher,
@@ -276,11 +271,7 @@ impl<
 		>::check_out(dest, what, context)
 	}
 
-	fn deposit_asset(
-		what: &MultiAsset,
-		who: &MultiLocation,
-		context: Option<&XcmContext>,
-	) -> XcmResult {
+	fn deposit_asset(what: &Asset, who: &Location, context: Option<&XcmContext>) -> XcmResult {
 		FungibleMutateAdapter::<
 			Fungible,
 			Matcher,
@@ -291,10 +282,10 @@ impl<
 	}
 
 	fn withdraw_asset(
-		what: &MultiAsset,
-		who: &MultiLocation,
+		what: &Asset,
+		who: &Location,
 		maybe_context: Option<&XcmContext>,
-	) -> result::Result<xcm_executor::Assets, XcmError> {
+	) -> result::Result<AssetsInHolding, XcmError> {
 		FungibleMutateAdapter::<
 			Fungible,
 			Matcher,
@@ -305,11 +296,11 @@ impl<
 	}
 
 	fn internal_transfer_asset(
-		what: &MultiAsset,
-		from: &MultiLocation,
-		to: &MultiLocation,
+		what: &Asset,
+		from: &Location,
+		to: &Location,
 		context: &XcmContext,
-	) -> result::Result<xcm_executor::Assets, XcmError> {
+	) -> result::Result<AssetsInHolding, XcmError> {
 		FungibleTransferAdapter::<Fungible, Matcher, AccountIdConverter, AccountId>::internal_transfer_asset(
 			what, from, to, context
 		)