BUG, DEP, DOC: Patch and Align Categorical's Sorting API
Clarifies the meaning of 'sort' in the context of `Categorical` to mean 'organization' rather than 'order',
as it is possible to call this method (as well as `sort_values`) when the `Categorical` is unordered.

Also patches a bug in `Categorical.sort_values` in which `na_position` was not being respected when
`ascending` was set to `True`. This commit aligns the behaviour with that of `Series`.

Finally, deprecates `sort` in favor of `sort_values`, which is in alignment with what was done with `Series` back in #10726.

Closes #12785.
