upgrade: allow for `sidedata` removal If the side-date feature is removed, we need to drop them. Differential Revision: https://phab.mercurial-scm.org/D6943

upgrade: allow upgrade to repository using sidedata Repository can now be migrated to support sidedata. More requirements and migration will be needed to actual side-data usage. This is a step in that direction. To test the feature, we leverage the test extension. It make sure the `update` part of the side-data migration actually works. Differential Revision: https://phab.mercurial-scm.org/D6942

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