Cannot use spawnegg without being able to build in region

WORLDGUARD-4080 - Reported by phoenix616

Currently spawneggs get blocked when you can't build in a region. This is a good behaviour but there is no way to allow usage of spawneggs without setting the build flag to allow. (You then would have to disable all other types of building with the other flags again) Ideally there would be a use_spawnegg flag which could be set to allow/deny usage of these eggs similarly to how vehicles work. (See the [bukkit listener](https://github.com/EngineHub/WorldGuard/blob/5180673878776ff4439d193df450cddae18e064b/worldguard-legacy/src/main/java/com/sk89q/worldguard/bukkit/listener/RegionProtectionListener.java#L333-L361), currently spawn eggs are just grouped into "others" and therefore use the normal build permissions)