Extract load_branch_decorations from todo_list_add_update_ref_commands so
it can be re-used in make_script_with_merges.
Since it can now be called multiple times, use non-static lists and place
it next to load_ref_decorations to re-use the decoration_loaded guard.
Signed-off-by: Nicolas Guichard <nicolas@guichard.eu> Acked-by: Phillip Wood <phillip.wood@dunelm.org.uk> Signed-off-by: Junio C Hamano <gitster@pobox.com>