Add typedefs for storage types (#4654)

* Add typedefs for storage types

* Fix after merge

substrate/client/src/light/backend.rs

@@ -27,7 +27,8 @@ use sp_core::ChangesTrieConfiguration;
 use sp_core::storage::{well_known_keys, ChildInfo, OwnedChildInfo};
 use sp_core::offchain::storage::InMemOffchainStorage;
 use sp_state_machine::{
-	Backend as StateBackend, TrieBackend, InMemoryBackend, ChangesTrieTransaction
+	Backend as StateBackend, TrieBackend, InMemoryBackend, ChangesTrieTransaction,
+	StorageCollection, ChildStorageCollection,
 };
 use sp_runtime::{generic::BlockId, Justification, Storage};
 use sp_runtime::traits::{Block as BlockT, NumberFor, Zero, Header, HasherFor};
@@ -36,7 +37,7 @@ use sp_blockchain::{Error as ClientError, Result as ClientResult};
 use sc_client_api::{
 	backend::{
 		AuxStore, Backend as ClientBackend, BlockImportOperation, RemoteBackend, NewBlockState,
-		StorageCollection, ChildStorageCollection, PrunableStateChangesTrieStorage,
+		PrunableStateChangesTrieStorage,
 	},
 	blockchain::{
 		HeaderBackend as BlockchainHeaderBackend, well_known_cache_keys,