SearchKit - Fix ORDER BY calculated fields when using GROUP BY

SearchKit - Fix ORDER BY calculated fields when using GROUP BY

Before: Calculated field functions were repeated verbabim in the SELECT, ORDER BY & GROUP BY clause,
this would cause mySql error when using FULL GROUP BY mode.

After: Calculated field function defined in SELECT clause, alias used in ORDER BY & GROUP BY.
No error when grouping by an ordering by the same calculated field.

Side-benefit: When selecting and ordering by RAND(), the selected random numbers will be in order,
as it's now the same random function used for both instead of a different one.