Sort crates before splitting them into groups (+ some improvements) (#12755)

* sort crates before splitting them into groups

this is useful so that crates always get routed to a specific group for a given version of the source code, which means that jobs for each batch can be reliably retried individually

* more verbose output

* misc improvements

* put uniq after sort

uniq filters by adjacent lines

* shellcheck

* rm useless backlashes

* handle edge case of no crates detected