[entity] move req.create_entity content to a cw_instantiate factory method on entity classes, so cube developpers will be able to easily customize instance creation
"""pre 3.6 bw compat"""# pylint: disable-msg=W0614,W0401fromwarningsimportwarnwarn('moved to cubicweb.mttransforms',DeprecationWarning,stacklevel=2)fromcubicweb.mttransformsimport*