Add hints for replacing some `maybe` usage with equivalent `traverse`

[googleson78]

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[ndmitchell]

Why is this desirable? The maybe function is more targeted so helps enforce types better.

[googleson78]

I personally find it desirable because the maybe usage is essentially reimplementing traverse, i.e. this is exactly the implementation of traverse.

I do agree that type inference is worse with this hint, and potentially (although I'm not sure when), this might cause ambiguity errors. Perhaps some optional group might be better here?

[ndmitchell]

Definitely not in base, which in general doesn't do generalization. But further down there is a set of hints called generalised, where maybe to traverse would fit nicely. Happy to take the patch if adjusted to go there.