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/testing/rococo-parachain/src/lib.rs

@@ -83,12 +83,14 @@ use xcm_executor::traits::JustTry;
 use pallet_xcm::{EnsureXcm, IsMajorityOfBody, XcmPassthrough};
 use polkadot_parachain_primitives::primitives::Sibling;
 use xcm::latest::prelude::*;
+#[allow(deprecated)]
+use xcm_builder::CurrencyAdapter;
 use xcm_builder::{
 	AccountId32Aliases, AllowExplicitUnpaidExecutionFrom, AllowTopLevelPaidExecutionFrom,
-	CurrencyAdapter, EnsureXcmOrigin, FixedWeightBounds, IsConcrete, NativeAsset,
-	ParentAsSuperuser, ParentIsPreset, RelayChainAsNative, SiblingParachainAsNative,
-	SiblingParachainConvertsVia, SignedAccountId32AsNative, SignedToAccountId32,
-	SovereignSignedViaLocation, TakeWeightCredit, UsingComponents,
+	EnsureXcmOrigin, FixedWeightBounds, IsConcrete, NativeAsset, ParentAsSuperuser, ParentIsPreset,
+	RelayChainAsNative, SiblingParachainAsNative, SiblingParachainConvertsVia,
+	SignedAccountId32AsNative, SignedToAccountId32, SovereignSignedViaLocation, TakeWeightCredit,
+	UsingComponents,
 };
 use xcm_executor::XcmExecutor;
 
@@ -345,6 +347,7 @@ pub type LocationToAccountId = (
 );
 
 /// Means for transacting assets on this chain.
+#[allow(deprecated)]
 pub type CurrencyTransactor = CurrencyAdapter<
 	// Use this currency:
 	Balances,