[opt] Simplify or_reduce(neg(x)) => or_reduce(x)

[cdleary]

This is a strict local improvement (or_reduce(neg(x)) depends on x instead of neg(x))

However, it also highlights an existing representational redundancy: for bits values, or_reduce(x) and ne(x, 0) both mean x != 0 and we don’t currently canonicalize between them. We may want to decide on a canonical nez form, or make some query helpers that recognize both as equivalent representations, but I think best done in a follow-up after some discussion, rather than as part of this change.