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

wpilibc/src/main/native/include/frc/SystemServer.h

@@ -0,0 +1,18 @@
+// 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 <networktables/NetworkTableInstance.h>
+
+namespace frc {
+
+class SystemServer {
+ public:
+  SystemServer() = delete;
+
+  static nt::NetworkTableInstance GetSystemServer();
+};
+
+}  // namespace frc