[flang][runtime] add SHAPE runtime interface (#94702)

Add SHAPE runtime API (will be used for assumed-rank, lowering is
generating other cases inline).

I tried to make it in a way were there is no dynamic allocation in the
runtime/deallocation expected to be inserted by inline code for arrays
that we know are small (lowering will just always stack allocate a rank
15 array to avoid dynamic stack allocation or heap allocation).