[OMPIRBuilder] Generate aggregate argument for parallel region outlined functions

Summary:
This patch modifies code generation in OpenMPIRBuilder to pass arguments
to the parallel region outlined function in an aggregate (struct),
besides the global_tid and bound_tid arguments. It depends on the
updated CodeExtractor (see D96854) for support. It mirrors functionality
of Clang codegen (see D102107).

Differential Revision: https://reviews.llvm.org/D110114