[migractions] remove any session related leftovers Also, the migration handler really wants a "repo" session anyway. This highlights a bug in unittest_wfobjs.test_duplicated_transition where an old connection is reused. It probably used to work because it was made of session + set_cnxset magic dust. Related to #3933480.

[session] provide missing apis to Connection From this point, Connection provides a superset of ClientConnection. Related to #3837233.

[connection] replace .running_dbapi_query with .hooks_in_progress The thing was badly named. It tries to help distinguish between queries issued directly by the programmer (e.g in the views: cnx.execute(...)) from queries issued from the hooks, operations ... or even the repository or the native source objects. It worked heuristically being associated with the security being disabled. We provide a better name and an implementation distinct from the security management methods. Related to #3933480.