[OpenMP][OMPT] Indicate loop schedule for worksharing-loop events (#97429)
Use more specific values from `ompt_work_t` to allow the tool identify
the schedule of a worksharing-loop. With this patch, the runtime will
report the schedule chosen by the runtime rather than necessarily the
schedule literally requested by the clause.
E.g., for guided + just one iteration per thread, the runtime would
choose and report static.
Fixes issue #63904