[test] silence warnings for unittest_entity by upgrading to new 3.19 API

Fix constraint sync during migration - restore constraints lost during merge in test schema. - use constraint_by_eid in BeforeDeleteCWConstraintHook as done in 3.17.14 for BeforeDeleteConstrainedByHook. Fixes handling of multiple constraints of the same type. - make sync_schema_props_perms() delete the CWConstraint entity instead of the constrained_by relation. In 3.19, the latter doesn't automatically result in the former just because the relation is composite. Simplify the constraint migration to delete all removed constraints and recreate new ones even if they share the same type; that optimization made the code more complicated for (AFAICT) no significant reason.

merge 3.18.4 into default server/test/unittest_migractions fails due to interaction between new constraint test (from 3.18) and composite deletion change (in 3.19).

Added tag cubicweb-version-3.18.4, cubicweb-debian-version-3.18.4-1, cubicweb-centos-version-3.18.4-1 for changeset 0176da9bc752

[test/data] Add missing 'add' permission on attribute Silences a warning introduced in 3.18.

[hooks/notification] Fix indentation Follow-up for changeset 1b8552265f3b "[hooks/notification] use a cnx not a session"

[devtools] deprecate CWTC.user()

minor cleanups

some copyright updates

[devtools] properly close open access on tearDown avoiding further warning about living sessions while the repo is turned off. The doc string says: The RepoAccess need to be closed to destroy the associated Session. TestCase usually take care of this aspect for the user. but that wasn't true until now.

[devtools] make comment (a bit) more readable

[devtools] avoid an internal deprecation warning websession and session are now one and the same.

[server/session] undeprecate session.anonymous_session It's not connection-specific.

[web/sessions] use session.sessionid instead of deprecated session.id

[repo] don't set cnxset when getting the session to close it and avoid warning about that. session._cnx.rollback won't do anything if it's not set and a newer connection is now created to run the session_close hook, so there is not need to set cnxset. Notice we have to take care about not trying to rollback the underlying cnx when the session is not 'session_handled' (i.e. bw compat mode). This case only occurs due to hackish things to keep bw compat in testlib.

[repo] handle connection explicitly when calling session open/close hooks

[hooks/syncschema] work with connections not sessions

[server/sources] {before,after}_entity_insertion wants a cnx not a session

[hooks/syncsources] use a cnx not a session

[hooks/notification] use a cnx not a session

[hooks/metadata] use a cnx not a session

[hooks/bookmark] use a cnx not a session

[hooks/workflow] use a cnx not a session

[hooks/email] use a cnx not a session

[hooks/integrity] use a cnx not a session

[hooks/security] let's use a connection, not a session

[server/sources/native] deal with connections, not sessions

[server] eschema_eid needs a connection, not a session