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/pallets/xcmp-queue/src/mock.rs

@@ -30,7 +30,9 @@ use sp_runtime::{
 	BuildStorage,
 };
 use xcm::prelude::*;
-use xcm_builder::{CurrencyAdapter, FixedWeightBounds, IsConcrete, NativeAsset, ParentIsPreset};
+#[allow(deprecated)]
+use xcm_builder::CurrencyAdapter;
+use xcm_builder::{FixedWeightBounds, IsConcrete, NativeAsset, ParentIsPreset};
 use xcm_executor::traits::ConvertOrigin;
 
 type Block = frame_system::mocking::MockBlock<Test>;
@@ -130,6 +132,7 @@ parameter_types! {
 }
 
 /// Means for transacting assets on this chain.
+#[allow(deprecated)]
 pub type LocalAssetTransactor = CurrencyAdapter<
 	// Use this currency:
 	Balances,