copies: move file input processsing early If we are to store the same kind of data outside of extra, we need to explicitly prepare them before that. On the long run, other storage (eg: sidedata) might use a different encoding to store this information, since the constraint from extra does not apply to it. Differential Revision: https://phab.mercurial-scm.org/D6937

copies: prepare changelog for more copies storage mode We want to store copies information in sidedata, the logic will be quite similar to the one used for extra, but sightly different (not in extra, no hash impact). We start with small refactoring to make our work easier and the coming changesets cleaners. Differential Revision: https://phab.mercurial-scm.org/D6936