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 <>

polkadot/runtime/westend/src/xcm_config.rs

@@ -39,14 +39,16 @@ use westend_runtime_constants::{
 	xcm::body::{FELLOWSHIP_ADMIN_INDEX, TREASURER_INDEX},
 };
 use xcm::latest::prelude::*;
+#[allow(deprecated)]
+use xcm_builder::CurrencyAdapter as XcmCurrencyAdapter;
 use xcm_builder::{
 	AccountId32Aliases, AllowExplicitUnpaidExecutionFrom, AllowKnownQueryResponses,
 	AllowSubscriptionsFrom, AllowTopLevelPaidExecutionFrom, ChildParachainAsNative,
-	ChildParachainConvertsVia, CurrencyAdapter as XcmCurrencyAdapter, DescribeBodyTerminal,
-	DescribeFamily, HashedDescription, IsConcrete, MintLocation, OriginToPluralityVoice,
-	SignedAccountId32AsNative, SignedToAccountId32, SovereignSignedViaLocation, TakeWeightCredit,
-	TrailingSetTopicAsId, UsingComponents, WeightInfoBounds, WithComputedOrigin, WithUniqueTopic,
-	XcmFeeManagerFromComponents, XcmFeeToAccount,
+	ChildParachainConvertsVia, DescribeBodyTerminal, DescribeFamily, HashedDescription, IsConcrete,
+	MintLocation, OriginToPluralityVoice, SignedAccountId32AsNative, SignedToAccountId32,
+	SovereignSignedViaLocation, TakeWeightCredit, TrailingSetTopicAsId, UsingComponents,
+	WeightInfoBounds, WithComputedOrigin, WithUniqueTopic, XcmFeeManagerFromComponents,
+	XcmFeeToAccount,
 };
 use xcm_executor::XcmExecutor;
 
@@ -72,6 +74,7 @@ pub type LocationConverter = (
 	HashedDescription<AccountId, DescribeFamily<DescribeBodyTerminal>>,
 );
 
+#[allow(deprecated)]
 pub type LocalAssetTransactor = XcmCurrencyAdapter<
 	// Use this currency:
 	Balances,