Port CA2G, SU2G, NI2G off implicit MAPL2 OpenMP aliases to explicit use MAPL

[tclune]

Problem

CA2G, SU2G, and NI2G all do `use MAPL` without `only`, and use `MAPL_get_num_threads` and `MAPL_get_current_thread` which are currently aliases re-exported by MAPL2. This is implicit and fragile.

Solution

Replace with explicit `use MAPL, only: MAPL_get_num_threads => get_num_threads, MAPL_get_current_thread => get_current_thread` as was done for DU2G in #410.

Related

• GOCART Port ReplenishAlarm.F90 off MAPL_MetaComp and MAPL_GetObjectFromGC #410 (DU2G already ported)
• MAPL #4730