Correct typing and adjustment for ifFn in noria backend

[JustusAdam]

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.