Minimal support for ERC2771 (GSNv2) (#2508)

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

contracts/mocks/ERC2771ContextMock.sol

@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "./ContextMock.sol";
+import "../metatx/ERC2771Context.sol";
+
+// By inheriting from ERC2771Context, Context's internal functions are overridden automatically
+contract ERC2771ContextMock is ContextMock, ERC2771Context {
+    constructor(address trustedForwarder) ERC2771Context(trustedForwarder) {}
+
+    function _msgSender() internal override(Context, ERC2771Context) view virtual returns (address) {
+        return ERC2771Context._msgSender();
+    }
+
+    function _msgData() internal override(Context, ERC2771Context) view virtual returns (bytes calldata) {
+        return ERC2771Context._msgData();
+    }
+}