Add utilities for CrossChain messaging (#3183)

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

contracts/vendor/polygon/IFxMessageProcessor.sol

@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+interface IFxMessageProcessor {
+    function processMessageFromRoot(
+        uint256 stateId,
+        address rootMessageSender,
+        bytes calldata data
+    ) external;
+}