Return values for sorting.
The transformed values should maintain the ordering between values within the array.
Return the indices that would sort this array.
The caller is responsible for not modifying these values in-place, so it is safe for implementors to give views on self.
Functions that use this (e.g. ExtensionArray.argsort) should ignore entries with missing values in the original array (according to self.isna()). This means that the corresponding entries in the returned array don’t need to be modified to sort correctly.