Correct typing and adjustment for `ifFn` in noria backend

Currently the calculated type for `ifFn` in the Noria backend is basically `A -> (A, A)`. This is technically incorrect and should instead be `A -> (Idx<0>, Idx<1>)`.
However with that typing we must later ensure that when we remove the `if`, we also adjust the column that the filters behind the if operate on, i.e. we need to adjust their labels.