[OpenMP] [OMPT] [7/8] Invoke tool-supplied callbacks before and after target...

[OpenMP] [OMPT] [7/8] Invoke tool-supplied callbacks before and after target launch and data transfer operations

Implemented RAII objects, initialized at target entry points, that
invoke tool-supplied callbacks. Updated status of target callbacks as
implemented.

Depends on D127365

Patch from John Mellor-Crummey <johnmc@rice.edu>
With contributions from:
Dhruva Chakrabarti <Dhruva.Chakrabarti@amd.com>
Jan-Patrick Lehr <janpatrick.lehr@amd.com>

Reviewed By: jdoerfert, dhruvachak, jplehr

Differential Revision: https://reviews.llvm.org/D127367