Implement sortslices, deprecate sortrows/sortcols (#28332)
As discussed on triage, `sortslices` is the higher dimensional extension
of `sortrows`/`sortcols`. The dimensions being specified are the dimensions
(and for higher dimensions the order of the dimensions) to slice along. See
the help text for an example of the higher dimensional behavior. Deprecate
sortrows/sortcols in favor of sortslices.
