sidedatacopies: teach upgrade about the new requirement The `debugformat` and `debugupgraderepo` command now detect the requirement. (upgrade to and from are not currently possible). Differential Revision: https://phab.mercurial-scm.org/D6946

sidedatacopies: add a new requirement for storing copies into sidedata The end goal is to have changesets centric sidedata information stored into changelog sidedata. This make it possible to use the changeset based copy tracing algorithm on any repository without affecting hashes. The actual implementation is coming. The feature is marked as experimental (do not use in production) until we stabilise details about the format. Differential Revision: https://phab.mercurial-scm.org/D6945

debugsidedata: small doc improvement The command has a mode to actually show the sidedata, but it wasn't documented. Differential Revision: https://phab.mercurial-scm.org/D6944

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

sidedata: use only changegroup3 if sidedata is in use This is necessary to exchange the flags over the wire (and within bundles). Differential Revision: https://phab.mercurial-scm.org/D6940

sidedata: apply basic but tight security around exchange We don't currently have code to deal with exchange between repository using sidedata and repository not using sidedata. Until we implement such code (eg: dropping side data when pushing to a non-sidedata repo) we prevent the two kind of repo to speak to each other. This is somewhere similar to what 'treemanifest' does. Note that sidedata exchange is broken unless one use changegroup v3 anyway. See next changeset for details. Differential Revision: https://phab.mercurial-scm.org/D6939

perf: use `setup` function in `perfdirstatewrite` The command seems to pre-date the introduction of the `setup` support in timer. We move the line that is obviously about benchmark setup in such `setup` function.

perf: document `perfdirstatewrite`