[flang][openacc] Support array section with constant lb or ub for data operand

Add support for array section with constant lower or upper bound.
The current lowering will trigger a TODO when the array is assumed size
or if the lower or upper bound is a variable.

Depends on D148721

Reviewed By: razvanlupusoru, jeanPerier

Differential Revision: https://reviews.llvm.org/D148748