Unified way to specify sort order for data prototype iteration

[Ruin0x11]

It is very common to want to specify what order to iterate the entries in data with when using data[...]:iter(). Currently, any code that wants a custom sorting order has to sort the iterator themselves, because the order of iteration for :iter() is undefined.

A very common pattern is to have an ordering field on the prototype, which is used by each sorting function. This was used to maintain vanilla compatibility where the sort order was based on a numeric ID.

I think the entries should be sorted by mod load order, and then this ordering field, for every possible data type. ordering would become a special prototype field like _id or _type available on all data types, because this concerns the :iter() function which is available for all possible data types. Generally when variants added new content like items, the numeric IDs would keep incrementing past the maximum ID of the last vanilla item, meaning the new items would always come after the vanilla items, so I think the mod load order for sorting is good as a default.

Also, ordering would be autopopulated based on the order of prototype addition if it's omitted.