[OpenMP] [OMPT] [8/8] Added lit tests for OMPT target callbacks

Added a new target ompt mode that depends on libomptarget OMPT support.
Added tests that verify callbacks for target regions, kernel launch,
and data transfer operations. All of them should pass on amdgpu using
make check-libomptarget.

Reviewed By: jplehr

Differential Revision: https://reviews.llvm.org/D127372