[OpenMP] Pass mapping names to add components in a user defined mapper

Summary:
Currently the mapping names are not passed to the mapper components that set up
the array region. This means array mappings will not have their names availible
in the runtime. This patch fixes this by passing the argument name to the region
correctly. This means that the mapped variable's name will be the declared
mapper that placed it on the device.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D99681