[flang] Explicitly map host associated symbols

Explicitly map host associated symbols in DoConcurrent with shared
locality-spec, clauses in OpenMP/OpenACC. The mapping of host-assoc
symbols is set to their parent SymbolBox. This is achieved through
a new interface function in the AbstractConverter.

This was already upstream for OpenMP.

This patch is part of the upstreaming effort from fir-dev branch.

Reviewed By: PeteSteinfeld

Differential Revision: https://reviews.llvm.org/D128518



Co-authored-by: Kiran Chandramohan <kiran.chandramohan@arm.com>