wireproto: split streamres into legacy and modern case A couple of commands currently require transmission of uncompressed frames with the old MIME type. Split this case from streamres into a new streamres_legacy class. Streamline the remaining code accordingly. Add a new flag to streamres to request uncompressed streams. This is useful for sending data that is already compressed like a pre-built bundle. Expect clients to support uncompressed data. For older clients, zlib will still be used. Differential Revision: https://phab.mercurial-scm.org/D1862