feat(orderBy): add support for custom comparators

Add an optional, 4th argument (`comparator`) for specifying a custom comparator function, used to
compare the values returned by the predicates. Omitting the argument, falls back to the default,
built-in comparator. The 3rd argument (`reverse`) can still be used for controlling the sorting
order (i.e. ascending/descending).

Additionally, the documentation has been expanded to cover the algorithm used by the built-in
comparator and a few more unit and e2e tests (unrelated to the change) have been added.

Helps with #12572 (maybe this is as close as we want to get).

Fixes #13238
Fixes #14455

Closes #5123
Closes #8112
Closes #10368

Closes #14468

Author: gkalpak