Remove Node.from_parent/.from_config indirection

[blueyed]

This is meant to go forward with #6571 (comment) / unblock the next release.

Ref: #5975 (comment)

Proof-of-concept: blueyed#143

TODO:

• this is based on the first addition of from_parent (Node from parent #5975), but I expect 8ba0b7b (Fix 6341 disallow session config in fromparent #6387) can be done in a similar way
• only allow particular classes (hierarchy)? (i.e. Module(parent=Item(…)) makes no sense)
• WIP POC RFC: remove config/session as possible parameters for node #6293 - but not clear how / if that is planned to be done like that still (should it be rebased/adjusted first?)

[RonnyPfannschmidt]

Not sure what you are doing here, this is failing the big picture at first glance and that won't do

[blueyed]

Ok, let's maybe move on then?
=> #6571 (comment)