[Clang][OpenMP][OMPIRBuilder] Move Clang's OpenMP Member/MemberOf flag helpers...

[Clang][OpenMP][OMPIRBuilder] Move Clang's OpenMP Member/MemberOf flag helpers into the OMPIRBuilder (#67844)

This patch seeks to move the following functions to the OMPIRBuilder:
 - getFlagMemberOffset
 - getMemberOfFlag
 - setCorrectMemberOfFlag

These small helper functions help set the end bits of the
OpenMPOffloadMappingFlags flag that correspond to the reserved segment
for OMP_MAP_MEMBER_OF.

They will be of use in the future for lowering MLIR types/values that
can contian members and can be lowered similarly to a structure or class
type within the OpenMPToLLVMIRTranslation step of the OpenMP dialects
lowering to LLVM-IR. In particular for Flang which currently uses this
flow. Types with descriptors like pointers/allocatables, and likely
derived types in certain cases can be lowered as if they were structures
with explicitly mapped members.