Contracts: Refactor API to use WeightMeter (#2943)

Update the Contracts API to use `WeightMeter`, as it simplifies the code
and makes it easier to reason about, rather than taking a mutable weight
or returning a tuple with the weight consumed

---------

Co-authored-by: Alexander Theißen <alex.theissen@me.com>

substrate/frame/contracts/src/migration/v09.rs

@@ -23,7 +23,9 @@ use crate::{
 	CodeHash, Config, Determinism, Pallet, Weight, LOG_TARGET,
 };
 use codec::{Decode, Encode};
-use frame_support::{pallet_prelude::*, storage_alias, DefaultNoBound, Identity};
+use frame_support::{
+	pallet_prelude::*, storage_alias, weights::WeightMeter, DefaultNoBound, Identity,
+};
 #[cfg(feature = "try-runtime")]
 use sp_runtime::TryRuntimeError;
 use sp_std::prelude::*;
@@ -87,7 +89,7 @@ impl<T: Config> MigrationStep for Migration<T> {
 		T::WeightInfo::v9_migration_step(T::MaxCodeLen::get())
 	}
 
-	fn step(&mut self) -> (IsFinished, Weight) {
+	fn step(&mut self, meter: &mut WeightMeter) -> IsFinished {
 		let mut iter = if let Some(last_key) = self.last_code_hash.take() {
 			v8::CodeStorage::<T>::iter_from(v8::CodeStorage::<T>::hashed_key_for(last_key))
 		} else {
@@ -106,10 +108,12 @@ impl<T: Config> MigrationStep for Migration<T> {
 			};
 			CodeStorage::<T>::insert(key, module);
 			self.last_code_hash = Some(key);
-			(IsFinished::No, T::WeightInfo::v9_migration_step(len))
+			meter.consume(T::WeightInfo::v9_migration_step(len));
+			IsFinished::No
 		} else {
 			log::debug!(target: LOG_TARGET, "No more contracts code to migrate");
-			(IsFinished::Yes, T::WeightInfo::v9_migration_step(0))
+			meter.consume(T::WeightInfo::v9_migration_step(0));
+			IsFinished::Yes
 		}
 	}