[connection] reinstall cnx.data as cnx.transaction_data Too much code expects self._cw.data to be session data. backout 9b2f68916474 Related to #2503918 Related to #2912807

[connection] give access to is_internal_session boolean Needed if we are to use this object like we currently do with session. Related to #2503918

[req] drop from_controller on non WebRequest object (Closes #2901079) The `controller` concept is purely a web things. It does not belong to generic `req` object. The `build_url` code is slightly changed to handle that. This probably requires extended cleanup later. This is a barely used and very internal API. No deprecation period

[connection] add logging method on connection If we are to use this object like we currently do with session, we need to have the logging method as a lot of code use them.

rename server.session.transaction into server.session.connection The ongoing rework of the API to access the database include the splitting of Session in two objects: The ``Session`` object will only hold credential (user) and global session data. A new object will publicly emerge to handle a database access. This object is named ``Connection`` since that the way database accessors with the same property are named in other system. So we renamed the ``Transaction`` object into ``Connection``. The ``Transaction`` object have already grown in the direction of something directly usable by generic code, but the name ``Transaction`` is ill suited as such object can be used for multiple database transaction in a row. Related to #2503918

[application] call req.set_session in application.main_handle_request The Session handling chain is no more responsible for calling req.set_session. It just returns a valid session and lets the caller link it to the Request. This opens the way to explicitly creating and closing a connection/transaction in ``application.main_handle_request``. Related to #2503918