[flang] lower RANK intrinsic (#93694)

First commit is reviewed in
https://github.com/llvm/llvm-project/pull/93682.

Lower RANK using fir.box_rank. This patches updates fir.box_rank to
accept box reference, this avoids the need of generating an assumed-rank
fir.load just for the sake of reading ALLOCATABLE/POINTER rank. The
fir.load would generate a "dynamic" memcpy that is hard to optimize
without further knowledge. A read effect is conditionally given to the
operation.