Remove the special-case that handled `fir.array_coor` with a
block-argument base by converting the element ref result (!fir.ref<i32>
-> memref<i32>) and leaving fir.array_coor alive.
Instead, we now always convert the base (!fir.ref<!fir.array<...>> ->
memref<...>) and compute the memref indices from the fir.array_coor
operands, so loads/stores become memref.load/store base[indices] and
fir.array_coor can be erased when it’s only used by memory ops.
2bd23d3fa6