[wpiutil] Add mDNS resolver and announcer (#3733)

wpiutil/src/main/native/cpp/MulticastHandleManager.h

@@ -0,0 +1,25 @@
+// 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 <memory>
+
+#include "wpi/DenseMap.h"
+#include "wpi/MulticastServiceAnnouncer.h"
+#include "wpi/MulticastServiceResolver.h"
+#include "wpi/UidVector.h"
+
+namespace wpi {
+struct MulticastHandleManager {
+  wpi::mutex mutex;
+  wpi::UidVector<int, 8> handleIds;
+  wpi::DenseMap<size_t, std::unique_ptr<wpi::MulticastServiceResolver>>
+      resolvers;
+  wpi::DenseMap<size_t, std::unique_ptr<wpi::MulticastServiceAnnouncer>>
+      announcers;
+};
+
+MulticastHandleManager& GetMulticastManager();
+}  // namespace wpi