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
[workspace]
members = ["hg-core", "hg-direct-ffi", "hg-cpython"]
exclude = ["chg", "hgcli"]