revlog: add a way to control sidedata changes during revlog.clone We introduce a new argument to pass a callable dealing with the side data logic. Since the side data are usually associated to higher level logic, the revlog code itself is unlikely to know that to do itself. As a result the higher level upgrade code will be responsible to decide what needs to changes. The lower level revlog.clone just get simple instructions to apply. Differential Revision: https://phab.mercurial-scm.org/D6941