base should export Typeable instances of its promoted data constructors

As initially reported in #8486 (closed), base does not export Typeable instances for its promoted data constructors, as witnessed by this:

{-# LANGUAGE DataKinds #-}

import Data.Typeable

x = typeRep (Proxy :: Proxy True)

yields

    No instance for (Typeable 'True) arising from a use of ‘typeRep’
    In the expression: typeRep (Proxy :: Proxy True)
    In an equation for ‘x’: x = typeRep (Proxy :: Proxy True)

It is indeed possible to derive these instances locally with standalone deriving, but that seems very problematic, should multiple modules do that independently.

Trac metadata

Trac field	Value
Version	7.8.2
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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