Initial commit of cross connect integration test project (#3434)

Adding as a separate project so current integration tests stay working.

crossConnIntegrationTests/src/main/native/cpp/mockds/MockDS.h

@@ -0,0 +1,23 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#pragma once
+
+#include <atomic>
+#include <thread>
+
+class MockDS {
+ public:
+  MockDS() = default;
+  ~MockDS() { Stop(); }
+  MockDS(const MockDS& other) = delete;
+  MockDS& operator=(const MockDS& other) = delete;
+
+  void Start();
+  void Stop();
+
+ private:
+  std::thread m_thread;
+  std::atomic_bool m_active{false};
+};