Add fn to check mainchain withdrew voted (#30)

Author: ducthotran2010

contracts/v0.8/ronin/IRoninGatewayV2.sol

@@ -131,6 +131,11 @@ interface IRoninGatewayV2 is MappedTokenConsumer {
     address _voter
   ) external view returns (bool);
 
+  /**
+   * @dev Returns whether the mainchain withdrew is casted by the voter.
+   */
+  function mainchainWithdrewVoted(uint256 _withdrawalId, address _voter) external view returns (bool);
+
   /**
    * @dev Returns whether the withdrawal is done on mainchain.
    */

contracts/v0.8/ronin/RoninGatewayV2.sol

@@ -252,6 +252,13 @@ contract RoninGatewayV2 is
     return _voted(depositVote[_chainId][_depositId], _voter);
   }
 
+  /**
+   * @dev {IRoninGatewayV2-mainchainWithdrewVoted}.
+   */
+  function mainchainWithdrewVoted(uint256 _withdrawalId, address _voter) external view returns (bool) {
+    return _voted(mainchainWithdrewVote[_withdrawalId], _voter);
+  }
+
   /**
    * @dev {IRoninGatewayV2-mainchainWithdrew}.
    */