[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.

Release notes
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.. toctree::
    :maxdepth: 1

    3.22
    3.21
    3.20
    3.19
    3.18
    3.17
    3.16
    3.15
    3.14