Floating instance for Data.Fixed

I'd like to contribute a Floating instance for Data.Fixed. I'm concerned that it may be undesirable for a reason that is not occurring to me; I'd be pleased to learn of any objections.

In concept it's this, although I will investigate if there is an implementation with better performance:

lift :: (HasResolution a) => (Double -> Double) -> Fixed a -> Fixed a
lift f = realToFrac . f . realToFrac

instance (HasResolution a) => Floating (Fixed a) where
  pi = realToFrac pi
  sin = lift sin
  -- etc, similar lift2 function for (**), logBase

Trac metadata

Trac field	Value
Version	7.10.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries/base
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CC	ekmett, hvr
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