FRAME: Unity Balance Conversion for Different IDs of Native Asset (#3659)

Introduce types to define 1:1 balance conversion for different relative
asset ids/locations of native asset.

Examples:
native asset on Asset Hub presented as `VersionedLocatableAsset` type in
the context of Relay Chain is
```
{
  `location`: (0, Parachain(1000)),
  `asset_id`: (1, Here),
}
```
and it's balance should be converted 1:1 by implementations of
`ConversionToAssetBalance` trait.

---------

Co-authored-by: Branislav Kontur <bkontur@gmail.com>

polkadot/xcm/xcm-builder/src/barriers.rs

@@ -322,6 +322,29 @@ impl<ParaId: IsSystem + From<u32>> Contains<Location> for IsChildSystemParachain
 	}
 }
 
+/// Matches if the given location is a system-level sibling parachain.
+pub struct IsSiblingSystemParachain<ParaId, SelfParaId>(PhantomData<(ParaId, SelfParaId)>);
+impl<ParaId: IsSystem + From<u32> + Eq, SelfParaId: Get<ParaId>> Contains<Location>
+	for IsSiblingSystemParachain<ParaId, SelfParaId>
+{
+	fn contains(l: &Location) -> bool {
+		matches!(
+			l.unpack(),
+			(1, [Junction::Parachain(id)])
+				if SelfParaId::get() != ParaId::from(*id) && ParaId::from(*id).is_system(),
+		)
+	}
+}
+
+/// Matches if the given location contains only the specified amount of parents and no interior
+/// junctions.
+pub struct IsParentsOnly<Count>(PhantomData<Count>);
+impl<Count: Get<u8>> Contains<Location> for IsParentsOnly<Count> {
+	fn contains(t: &Location) -> bool {
+		t.contains_parents_only(Count::get())
+	}
+}
+
 /// Allows only messages if the generic `ResponseHandler` expects them via `expecting_response`.
 pub struct AllowKnownQueryResponses<ResponseHandler>(PhantomData<ResponseHandler>);
 impl<ResponseHandler: OnResponse> ShouldExecute for AllowKnownQueryResponses<ResponseHandler> {

polkadot/xcm/xcm-builder/src/lib.rs

@@ -37,8 +37,8 @@ mod barriers;
 pub use barriers::{
 	AllowExplicitUnpaidExecutionFrom, AllowKnownQueryResponses, AllowSubscriptionsFrom,
 	AllowTopLevelPaidExecutionFrom, AllowUnpaidExecutionFrom, DenyReserveTransferToRelayChain,
-	DenyThenTry, IsChildSystemParachain, RespectSuspension, TakeWeightCredit, TrailingSetTopicAsId,
-	WithComputedOrigin,
+	DenyThenTry, IsChildSystemParachain, IsParentsOnly, IsSiblingSystemParachain,
+	RespectSuspension, TakeWeightCredit, TrailingSetTopicAsId, WithComputedOrigin,
 };
 
 mod controller;