Tweak future opaque ty pretty printing 1. The `Return` type of a generator doesn't need to be a lang item just for diagnostic printing of types 2. We shouldn't suppress the `Output = Ty` of a opaque future if the type is a int or float var.
Tweak future opaque ty pretty printing 1. The `Return` type of a generator doesn't need to be a lang item just for diagnostic printing of types 2. We shouldn't suppress the `Output = Ty` of a opaque future if the type is a int or float var.