[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
[MESSAGES CONTROL]
disable-msg = C0301
[VARIABLES]
# Enable / disable this checker
enable-variables = yes
additional-builtins = _, display_name
[BASIC]
required-attributes=
attr-rgx = (w|[a-z_][a-z0-9_]{2,30})
variable-rgx = (w|[a-z_][a-z0-9_]{2,30})$
argument-rgx = (w|[a-z_][a-z0-9_]{2,30})$
[TYPECHECK]
generated-members=debug,info,notice,warning,error,critical,exception