`get_fields`, `yield_fields`, `get_field_values` should have an optional argument to include properties, descriptors, and vars

[smarie]

It would be very convenient that anyone can use thes helper functions on any class (not necessary classes with fields).

In particular when "view" properties are defined it would be convenient that get_field_values includes them. See for example https://stackoverflow.com/questions/62516472/python-getters-setters-and-manipulating-fields/

Also, we should clarify in the readme that get_field_values is to be preferred over vars when no constructor exists, since it guarantees that the fields with default values/factories are all created if not yet done.