Split full name into separate first and last name fields in address entity

[dlhck]

tl;dr; Regarding addresses: Make fullName read-only. Introduce firstName and lastName fields. fullName field will be calculated by the two newly introduced fields to keep compatibility with existing functionality.

Currently, the full name of a person in the address is stored in a single field. That is the simplest way because it gives kind of a flexibility but could lead to major problems in third-party systems. That's why I would propose introducing the fields firstName and lastName and changing the fullName field to a calculated, read-only field. That keeps the compatibility with plugins and other functionality but enables a lot more options in other places.

Separate first and last name fields are especially necessary when connecting fulfillment providers, delivery providers or ERP systems. These kinds of systems also store names in separate fields.