Turn displayed components into pseudo fields

Problem/Motivation

A few components like the list of opening instances on the calendar entity or the slots and booking button on opening instance entities are hard coded and always rendered and displayed when viewing those entities.

This should be configurable, so that the site builder can decide if and where those components are displayed. And at the same time, those components would also be useful as fields in views. Both of those requirements can be delivered with the same solution.

Proposed resolution

Turn the building of those components into a service. Add pseudo fields for those components and only call the rendering from the service when configured accordingly.

Then, also add them as views fields, using the same code from that service.