[OpenMP] Add Support for Mapping Names in Libomptarget RTL

Summary:
This patch adds basic support for priting the source location and names for the
mapped variables. This patch does not support names for custom mappers. This is
based on D89802. The names information currently will be printed out only in
debug mode or using env LIBOMPTARGET_INFO during execution. But the information
is added when availible to the Device and Private data structures. To get the
information out the code must be built with debug symbols on using -g or
-Rpass=openmp-opt

Reviewers: jdoerfert

Differential Revision: https://reviews.llvm.org/D90172