[server/session] fix a couple typos in doc strings

[server/migractions] finish migration to repoapi objects Changeset 241b1232ed7f (Use repoapi instead of dbapi for cwctl shell, upgrade and db-init) only did half of the job. It left the migration handler with both a session (cubicweb.server.session.Session) and a cnx (cubicweb.repoapi.ClientConnection) attribute with different ideas of what Connection they were talking to. With this change, we: - make the caller responsible of disabling security on the Connection if it wants to - turn mih.session into an actual attribute, set on __init__ - same for cnx (the client connection) - drop the "lazy connection" logic, and establish the connection up-front - always go through the connection instead of the session when we need to talk to the db

[server] use the ClientConnection directly now that it has more methods available Gets rid of ugly self.cnx._cnx.

[repoapi] add security/hook control and system_sql Just redirect these methods to the repo-side Connection.

[predicates] fix thinko in doc strings Replace "e.g." with more appropriate "i.e.". These are not examples.

[web/basecomponents] remove EtypeRestrictionComponent Closes #3119951

[ldapparser, book] document additional error causes

[js] remove leftover dead code in loadxhtml form.callback support was removed in changeset 68cde7431c2c, but some signs of it remained.

[web] Avoid using an empty dict as default parameter of 'CubicWebRequestBase'. Also update the related docstring of the __init__ method.

[schema] fix composite deletion handling Do not delete component entities if the composite is not deleted in the same transaction. Deletion semantics are thus: if the composite is deleted, the components are deleted. Closes #3463112.