Move large tuples to a separate module in base

Quoting from my message to ghc-devs@:

It occurred to me that rather than moving just these instances to a new module, we could move the large tuples themselves to a new module Data.LargeTuple and put the instances there. The Prelude would reexport the large tuples, so there would be no user-visible change. According to my experiments, GHC should never have to read the Data.LargeTuple interface file unless a program actually mentions a large tuple type, which is presumably rare. We could then also extend the existing instances for Eq, Show, etc., which are currently only provided through 15-tuples.

A nontrivial aspect of this change is that tuples are wired-in types, and they currently all live in the ghc-prim package. I'm actually not sure why they need to be wired-in rather than ordinary types with a funny-looking name. In any case I need to look into this further, but the difficulties here don't seem to be insurmountable.

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Trac field	Value
Version	8.1
Type	Task
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries/base
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