Allow capping the amount of work performed when deleting a child trie (#7671)

* Allow Backend::for_keys_in_child_storage to be aborted by the closure

* Ext::kill_child_storage now takes an upper limit for backend deletion

* Add Storage::storage_kill_limited() runtime interface

* review: Use a new version of kill_storage instead of a new interface

* review: Simplify boolean expression

Co-authored-by: cheme <emericchevalier.pro@gmail.com>

* review: Rename for_keys_in_child_storage

Co-authored-by: cheme <emericchevalier.pro@gmail.com>

substrate/frame/contracts/src/rent.rs

@@ -240,6 +240,7 @@ where
 				<ContractInfoOf<T>>::remove(account);
 				child::kill_storage(
 					&alive_contract_info.child_trie_info(),
+					None,
 				);
 				<Module<T>>::deposit_event(RawEvent::Evicted(account.clone(), false));
 				None
@@ -263,6 +264,7 @@ where
 
 				child::kill_storage(
 					&alive_contract_info.child_trie_info(),
+					None,
 				);
 
 				<Module<T>>::deposit_event(RawEvent::Evicted(account.clone(), true));