Add isHardcore API to check if the server is in hardcore mode or not. Adds BUKKIT-2707

By: EvilSeph <evilseph@gmail.com>

paper-api/src/main/java/org/bukkit/Bukkit.java

@@ -243,6 +243,10 @@ public final class Bukkit {
         return server.getAllowFlight();
     }
 
+    public static boolean isHardcore() {
+        return server.isHardcore();
+    }
+
     public static void shutdown() {
         server.shutdown();
     }

paper-api/src/main/java/org/bukkit/Server.java

@@ -475,6 +475,13 @@ public interface Server extends PluginMessageRecipient {
      */
     public boolean getAllowFlight();
 
+    /**
+     * Gets whether the server is in hardcore mode or not.
+     *
+     * @return Whether this server is in hardcore mode or not.
+     */
+    public boolean isHardcore();
+
     /**
      * Gets whether to use vanilla (false) or exact behaviour (true).
      *