Top-level sort vocabulary for a manifest. The directions list is fixed — Ash's sort directions don't vary per resource or app config.
@type direction() :: :asc | :desc | :asc_nils_first | :asc_nils_last | :desc_nils_first | :desc_nils_last
@type t() :: %Ash.Info.Manifest.SortCapabilities{ custom: map(), directions: [direction()] }