sidedatacopies: write copies information in sidedata when applicable If the format of the repository indicate it stores copies information into changeset's sidedata, then we actually write that information into sidedata at commit time. It will be put to use in later changesets. Currently, we store all field unconditionally, but that is likely to change in the future for the sake of efficiency. Differential Revision: https://phab.mercurial-scm.org/D6950