[flang][openacc] Add basic lowering for OpenACC declare construct in module

This patch adds the skeleton and the basic lowering for OpenACC declare
construct when located in the module declaration. This patch just lower the
create clause with or without modifier. Other clause and global descrutor
lowering will come in follow up patches to keep this one small enough for
review.

Reviewed By: razvanlupusoru

Differential Revision: https://reviews.llvm.org/D156266