Native: store ID->hash mapping for native contracts too

This is an omission of neo-project#2807, even though native hashes are well-known
GetContractById better be symmetric for all contracts. Related to
nspcc-dev/neo-go#2837.

src/Neo/SmartContract/Native/ContractManagement.cs

@@ -116,6 +116,7 @@ internal override async ContractTask OnPersist(ApplicationEngine engine)
                     Hash = contract.Hash,
                     Manifest = contract.Manifest
                 }));
+                engine.Snapshot.Add(CreateStorageKey(Prefix_ContractHash).AddBigEndian(contract.Id), new StorageItem(contract.Hash.ToArray()));
                 await contract.Initialize(engine);
             }
         }