Add FungibleAdapter (#2684)

In the move from the old `Currency` traits to the new `fungible/s`
family of traits, we already had the `FungiblesAdapter` and
`NonFungiblesAdapter` for multiple fungible and non fungible assets
respectively. However, for handling only one fungible asset, we were
missing a `FungibleAdapter`, and so used the old `CurrencyAdapter`
instead. This PR aims to fill in that gap, and provide the new adapter
for more updated examples.

I marked the old `CurrencyAdapter` as deprecated as part of this PR, and
I'll change it to the new `FungibleAdapter` in a following PR.
The two stages are separated so as to not bloat this PR with some name
fixes in tests.

---------

Co-authored-by: command-bot <>

cumulus/parachains/runtimes/contracts/contracts-rococo/src/xcm_config.rs

@@ -37,14 +37,16 @@ use polkadot_parachain_primitives::primitives::Sibling;
 use polkadot_runtime_common::xcm_sender::ExponentialPrice;
 use sp_runtime::traits::AccountIdConversion;
 use xcm::latest::prelude::*;
+#[allow(deprecated)]
+use xcm_builder::CurrencyAdapter;
 use xcm_builder::{
 	AccountId32Aliases, AllowExplicitUnpaidExecutionFrom, AllowKnownQueryResponses,
-	AllowSubscriptionsFrom, AllowTopLevelPaidExecutionFrom, CurrencyAdapter,
-	DenyReserveTransferToRelayChain, DenyThenTry, EnsureXcmOrigin, FixedWeightBounds, IsConcrete,
-	NativeAsset, ParentAsSuperuser, ParentIsPreset, RelayChainAsNative, SiblingParachainAsNative,
-	SiblingParachainConvertsVia, SignedAccountId32AsNative, SignedToAccountId32,
-	SovereignSignedViaLocation, TakeWeightCredit, TrailingSetTopicAsId, UsingComponents,
-	WithComputedOrigin, WithUniqueTopic, XcmFeeManagerFromComponents, XcmFeeToAccount,
+	AllowSubscriptionsFrom, AllowTopLevelPaidExecutionFrom, DenyReserveTransferToRelayChain,
+	DenyThenTry, EnsureXcmOrigin, FixedWeightBounds, IsConcrete, NativeAsset, ParentAsSuperuser,
+	ParentIsPreset, RelayChainAsNative, SiblingParachainAsNative, SiblingParachainConvertsVia,
+	SignedAccountId32AsNative, SignedToAccountId32, SovereignSignedViaLocation, TakeWeightCredit,
+	TrailingSetTopicAsId, UsingComponents, WithComputedOrigin, WithUniqueTopic,
+	XcmFeeManagerFromComponents, XcmFeeToAccount,
 };
 use xcm_executor::XcmExecutor;
 
@@ -77,6 +79,7 @@ pub type LocationToAccountId = (
 );
 
 /// Means for transacting the native currency on this chain.
+#[allow(deprecated)]
 pub type CurrencyTransactor = CurrencyAdapter<
 	// Use this currency:
 	Balances,