Add API for ambient mob spawn limit. Adds BUKKIT-2765

By: Travis Watkins <amaranth@ubuntu.com>

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

@@ -371,6 +371,10 @@ public final class Bukkit {
         return server.getWaterAnimalSpawnLimit();
     }
 
+    public static int getAmbientSpawnLimit() {
+        return server.getAmbientSpawnLimit();
+    }
+
     public static boolean isPrimaryThread() {
         return server.isPrimaryThread();
     }