Add option to sort by an attribute before validation of has_many members with indexed errors

[André Hester]

I would like to introduce an option order_before_validation for has_many associations:
If you add new objects via an Rails API to an `has_many` association via nested attributes and you would like to keep the order of the collection sorted by an attribute the matching of the errors via `index_errors` to form input´s can be hard. You can add an `order` attribute that you set manually on client side after re-ordering or adding new items and order the collection before validation. Validation errors can easily assigned to the associated input´s in the form via the index.

Do you think it it worthy merging into Rails Core?

https://github.com/andre1810/rails/tree/order_before_validation_option

Best regards

André