[hal] Add high level way of getting systemserver NT instance (#7683)

wpilibc/src/main/native/cpp/SystemServer.cpp

@@ -0,0 +1,15 @@
+// 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.
+
+#include "frc/SystemServer.h"
+
+#include <hal/SystemServer.h>
+
+namespace frc {
+
+nt::NetworkTableInstance SystemServer::GetSystemServer() {
+  return nt::NetworkTableInstance{HAL_GetSystemServerHandle()};
+}
+
+}  // namespace frc