SPIGOT-2398: Armor stands still need to be treated special for gravity

By: md_5 <git@md-5.net>

paper-server/src/main/java/org/bukkit/craftbukkit/entity/CraftArmorStand.java

@@ -149,6 +149,13 @@ public class CraftArmorStand extends CraftLivingEntity implements ArmorStand {
         getHandle().setBasePlate(!basePlate);
     }
 
+    @Override
+    public void setGravity(boolean gravity) {
+        super.setGravity(gravity);
+        // Armor stands are special
+        getHandle().noclip = !gravity;
+    }
+
     @Override
     public boolean isVisible() {
         return !getHandle().isInvisible();