[hooks] build EnsureSymmetricRelations{Add,Delete} dynamically
Instead of setting the __select__ attribute at registration time, which
confuses the filterable_selectors cache when running different tests (with
different schemas) in the same process, just make entirely new classes.
Closes #8785708.
Document: cubicweb-doc
Title: CubicWeb documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/cubicweb-documentation/index.html
Files: /usr/share/doc/cubicweb-documentation/*.html