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Previously if we had f |> co where `f` had arity type `ABot N` and `co` had arity M and M < N, `arityType` would return `ABot M` which is wrong, because `f` is only known to diverge when applied to `N` args, as described in Note [ArityType]: If at = ABot n, then (f x1..xn) definitely diverges. Partial applications to fewer than n args may *or may not* diverge. This caused incorrect eta expansion in the simplifier, causing #16066. We now return `ATop M` for the same expression so the simplifier can't assume partial applications of `f |> co` is divergent. A regression test T16066 is also added.Previously if we had f |> co where `f` had arity type `ABot N` and `co` had arity M and M < N, `arityType` would return `ABot M` which is wrong, because `f` is only known to diverge when applied to `N` args, as described in Note [ArityType]: If at = ABot n, then (f x1..xn) definitely diverges. Partial applications to fewer than n args may *or may not* diverge. This caused incorrect eta expansion in the simplifier, causing #16066. We now return `ATop M` for the same expression so the simplifier can't assume partial applications of `f |> co` is divergent. A regression test T16066 is also added.
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