Fix situation with Data.Enum and Data.Bounded in base

@Bodigrim writes in !11347 (closed)

The proposal meant to introduce Data.Bounded for class Bounded and Data.Enum for class Enum. Yet in base-4.20 I observe Data.Enum with both type classes, but no Data.Bounded at all. There is neither changelog nor @since pragma. Even more confusingly, this MR is still unmerged. What's happening?

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