[Offload][OpenMP] Decouple device property accesses from Plugin Interface (#231932)
Removes all calls to the PluginInterface to get device specific
properties:
- Some were reading only env vars and were moved directly to
libomptarget.
- A few new properties were adedd to be accessible through
olGetDeviceInfo.
- A few others were derived in libomptarget.
Assisted by Claude.