[flang][HLFIR] lower hlfir.declare of assumed-ranks (#93468)

hlfir.declare is in charge of ensuring that the lower bounds of its
"hlfir entity" output are the ones of the source program. For
non-allocatable/non-pointer assumed-ranks where the input descriptor
lower bounds may not be ones, the hlfir.declare needs to be lowered to
an hlfir.rebox_assumed_rank to set the lower bounds to ones.