[evm] ExternalResult does not pass the reason string correctly

[junkil-park]

See ExternalCall.move.

As the "TODO" says, it's expected to revert with the reason string which come from the callee. However, it reverts without any string.

// TODO: The following lines results in reverting without a reason string.
//       However, it is expected to revert with "ERC721ReceiverMock: reverting".
 let reason = ExternalResult::unwrap_err_reason(result);
 abort_with(reason);