feat(ctb): Copy over Lib_CrossDomainUtils for testing

packages/contracts-bedrock/contracts/libraries/LegacyCrossDomainUtils.sol

+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.9;
+
+// Importing from the legacy contracts package causes issues with the build of the contract bindings
+// so we just copy the library here from
+// /packages/contracts/contracts/libraries/bridge/Lib_CrossDomainUtils.sol at commit
+// 7866168c
+/**
+ * @title LegacyCrossDomainUtils
+ */
+library LegacyCrossDomainUtils {
+    /**
+     * Generates the correct cross domain calldata for a message.
+     * @param _target Target contract address.
+     * @param _sender Message sender address.
+     * @param _message Message to send to the target.
+     * @param _messageNonce Nonce for the provided message.
+     * @return ABI encoded cross domain calldata.
+     */
+    function encodeXDomainCalldata(
+        address _target,
+        address _sender,
+        bytes memory _message,
+        uint256 _messageNonce
+    ) internal pure returns (bytes memory) {
+        return
+            abi.encodeWithSignature(
+                "relayMessage(address,address,bytes,uint256)",
+                _target,
+                _sender,
+                _message,
+                _messageNonce
+            );
+    }
+}