Implement a sane storage default mapping

Problem/Motivation

DatabaseStorageControllerNG accesses field properties hardcoded in following methods:

• DatabaseStorageControllerNG::mapToDataStorageRecord()
• DatabaseStorageControllerNG::mapToRevisionStorageRecord()
• DatabaseStorageControllerNG::mapToStorageRecord()
• DatabaseStorageControllerNG::attachPropertyData()

In all this locations ->value is used to either read or write a field property.
This is ugly because there's no rule that defines that a field has to have a value field property.
E.g. EntityReferenceItem defines target_id and entity as properties.
Thus EntityReferenceItem has some mapping in its getter / setter methods to deal with value.
However, we really should provide a sane way to define what properties have to be handled by the storage controler.
Open question: Is there the posibility that e.g. EntityReferenceItem can define more than one property to be stored / read?

"Related Issues":

• #1847588-30: Implement the new entity field API for the Entity-Reference field type
• #1818556-176: Convert nodes to the new Entity Field API

Proposed resolution

Remaining tasks

User interface changes

API changes