ArbDebug: add overwriteContractCode interface

Author: KolbyML

ArbDebug.sol

@@ -12,6 +12,9 @@ interface ArbDebug {
     /// @notice Caller becomes a chain owner
     function becomeChainOwner() external;
 
+    /// @notice Overwrite an existing contract's code
+    function overwriteContractCode(address target, bytes calldata newCode) external returns (bytes memory oldCode);
+
     /// @notice Emit events with values based on the args provided
     function events(bool flag, bytes32 value) external payable returns (address, uint256);