Fix denormalisation of single map (like) property fields

Problem/Motivation

I am working on a feature that denormalizes entity_type_behavior field, which turns out is problematic.

Steps to reproduce

Normalise and denormalise entity_type_behavior field or one that has a single property of type map.
I've provided automated test with existing test field.
This was painful for quite some time and various workarounds have been introduced, such as ✨ Compatibility with paragraph behaviors Fixed

Proposed resolution

Process the field value in the denormalisation method in a way that reverses the effects of the flatting done in the normalisation.
Do it in a safe way that avoids undesired effects.

Remaining tasks

Review

User interface changes

None

API changes

None

Data model changes

None

Release notes snippet