Expose ChargedAmount (paritytech#13488) (#37)

* Expose `ChargedAmount`

(cherry picked from commit 376ada8)

frame/contracts/src/chain_extension.rs

@@ -71,7 +71,6 @@
 //! on how to use a chain extension in order to provide new features to ink! contracts.
 
 use crate::{
-	gas::ChargedAmount,
 	wasm::{Runtime, RuntimeCosts},
 	Error,
 };
@@ -80,7 +79,7 @@ use frame_support::weights::Weight;
 use sp_runtime::DispatchError;
 use sp_std::{marker::PhantomData, vec::Vec};
 
-pub use crate::{exec::Ext, Config};
+pub use crate::{exec::Ext, gas::ChargedAmount, Config};
 pub use frame_system::Config as SysConfig;
 pub use pallet_contracts_primitives::ReturnFlags;