Make $! representation-polymorphic

Currently,

($) :: forall r a (b :: TYPE r). (a -> b) -> a -> b

but

($!) :: (a -> b) -> a -> b

It seems fairly obvious that we should generalize ($!).

Trac metadata

Trac field	Value
Version	8.2.2
Type	Task
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Core Libraries
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