pallet-asset-conversion: Decoupling Native Currency Dependancy (#2031)

closes https://github.com/paritytech/polkadot-sdk/issues/1842

Decoupling Pallet from the Concept of Native Currency

Currently, the pallet is intrinsically linked with the concept of native
currency, requiring users to provide implementations of the
`fungible::*` and `fungibles::*` traits to interact with native and non
native assets. This incapsulates some non-related to the pallet
complexity and makes it less adaptable in contexts where the native
currency concept is absent.

With this PR, the dependence on `fungible::*` for liquidity-supplying
assets has been removed. Instead, the native and non-native currencies'
handling is now overseen by a single type that implements the
`fungibles::*` traits. To simplify this integration, types have been
introduced to facilitate the creation of a union between `fungible::*`
and `fungibles::*` implementations, producing a unified `fungibles::*`
type.

One of the reasons driving these changes is the ambition to create a
more user-friendly API for the `SwapCredit` implementation. Given that
it interacts with two distinct credit types from `fungible` and
`fungibles`, a unified type was introduced. Clients now manage potential
conversion failures for those credit types. In certain contexts, it's
vital to guarantee that operations are fail-safe, like in this impl -
[PR](https://github.com/paritytech/polkadot-sdk/pull/1845), place in
[code](https://github.com/paritytech/polkadot-sdk/blob/20b85a5fada8f55c98ba831964f5866ffeadf4da/cumulus/primitives/utility/src/lib.rs#L429).

Additional Updates:
- abstracted the pool ID and its account derivation logic via trait
bounds, along with common implementation offerings;
- removed `inc_providers` on a pool creation for the pool account;
- benchmarks:
-- swap complexity is N, not const;
-- removed `From<u128> + Into<u128>` bound from `T::Balance`;
-- removed swap/liquidity/.. amount constants, resolve them dynamically
based on pallet configuration;
-- migrated to v2 API;
- `OnUnbalanced` handler for the pool creation fee, replacing direct
transfers to a specified account ID;
- renamed `MultiAssetId` to `AssetKind` aligning with naming across
frame crates;

related PRs:
- (depends) https://github.com/paritytech/polkadot-sdk/pull/1677
- (caused) https://github.com/paritytech/polkadot-sdk/pull/2033
- (caused) https://github.com/paritytech/polkadot-sdk/pull/1876

---------

Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>
Co-authored-by: Liam Aharon <liam.aharon@hotmail.com>

cumulus/parachains/runtimes/assets/asset-hub-rococo/src/xcm_config.rs

@@ -56,9 +56,6 @@ use xcm_builder::{
 };
 use xcm_executor::{traits::WithOriginFilter, XcmExecutor};
 
-#[cfg(feature = "runtime-benchmarks")]
-use cumulus_primitives_core::ParaId;
-
 parameter_types! {
 	pub const TokenLocation: MultiLocation = MultiLocation::parent();
 	pub const RelayNetwork: NetworkId = NetworkId::Rococo;
@@ -66,8 +63,8 @@ parameter_types! {
 	pub UniversalLocation: InteriorMultiLocation =
 		X2(GlobalConsensus(RelayNetwork::get()), Parachain(ParachainInfo::parachain_id().into()));
 	pub UniversalLocationNetworkId: NetworkId = UniversalLocation::get().global_consensus().unwrap();
-	pub TrustBackedAssetsPalletLocation: MultiLocation =
-		PalletInstance(<Assets as PalletInfoAccess>::index() as u8).into();
+	pub AssetsPalletIndex: u32 = <Assets as PalletInfoAccess>::index() as u32;
+	pub TrustBackedAssetsPalletLocation: MultiLocation = PalletInstance(AssetsPalletIndex::get() as u8).into();
 	pub ForeignAssetsPalletLocation: MultiLocation =
 		PalletInstance(<ForeignAssets as PalletInfoAccess>::index() as u8).into();
 	pub PoolAssetsPalletLocation: MultiLocation =
@@ -672,32 +669,6 @@ impl pallet_assets::BenchmarkHelper<MultiLocation> for XcmBenchmarkHelper {
 	}
 }
 
-#[cfg(feature = "runtime-benchmarks")]
-pub struct BenchmarkMultiLocationConverter<SelfParaId> {
-	_phantom: sp_std::marker::PhantomData<SelfParaId>,
-}
-
-#[cfg(feature = "runtime-benchmarks")]
-impl<SelfParaId> pallet_asset_conversion::BenchmarkHelper<MultiLocation, MultiLocation>
-	for BenchmarkMultiLocationConverter<SelfParaId>
-where
-	SelfParaId: frame_support::traits::Get<ParaId>,
-{
-	fn asset_id(asset_id: u32) -> MultiLocation {
-		MultiLocation {
-			parents: 1,
-			interior: X3(
-				Parachain(SelfParaId::get().into()),
-				PalletInstance(<Assets as PalletInfoAccess>::index() as u8),
-				GeneralIndex(asset_id.into()),
-			),
-		}
-	}
-	fn multiasset_id(asset_id: u32) -> MultiLocation {
-		Self::asset_id(asset_id)
-	}
-}
-
 /// All configuration related to bridging
 pub mod bridging {
 	use super::*;