This set explicitly lists all the requirements that "stream clone" will
preserve. Any other one will not be preserved.
The role of listing the relevant one was previously filled by
repo.supportedformat, but it seems clearer to use that such global and
explicit set. The repo.supportedformat attribute will be cleaned up in a later
The true meaning of repo.supportedformat vs repo._basesupported was lost
over time so, the content is currently bad. For example, dirstate-v2 is
currently considered relevant to the stream clone, or internal phase is
missing. We kept the same content in this changeset and we will fix them later.