cubicweb-container #3589827 use plain rdefs everywhere [not validated]

This is an old nagging design flaw: we use etypes and rtypes sets to shape the container.
When people start playing with rtypes that have rdefs in the container, at the border, or in outer space, things fall a bit apart.

priorityimportant
typeenhancement
done in2.4.0
load1.000
load left0.000
closed by#8f804ee46af4 Switch to rdefs to define the container structure, and make the container relation reflexive
patchConfig: tighten .border_rdefs [applied]Switch to rdefs to define the container structure, and make the container relation reflexive [applied][config] Introduce container rdefs computation [applied]
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