Implement a reverse lexicographic IEF-ID sort on entities before saving them to ensure inside-out saving

Problem/Motivation

There is a plethora of issues for nested IEFs. Like:
- Created entities of lower levels are lost
- Entities of lower levels throw when saved twice

Some, mabe all of this may be explained by the non-well-defined nature of the entities in \Drupal\inline_entity_form\WidgetSubmit::doSubmit.
That above issues depended on the order of subform submission, supports that conjecture.

Proposed resolution

Implement a reverse lexicographic IEF-ID sort on entities before saving them to ensure inside-out saving

Remaining tasks

User interface changes

API changes

Data model changes