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TH: make `Lift` and `TExp` levity-polymorphic

Alec Theriault requested to merge harpocrates/ghc:levity-polymorphic-lift into master

Besides the obvious benefits of being able to manipulate TExp's of unboxed types, this also simplified -XDeriveLift all while making it more capable.

  • ghc-prim is explicitly depended upon by template-haskell

  • The following TH things are parametrized over RuntimeRep:

    • TExp(..)
    • unTypeQ
    • unsafeTExpCoerce
    • Lift(..)

  • The following instances have been added to Lift:

    • Int#, Word#, Float#, Double#, Char#, Addr#
    • unboxed tuples of lifted types up to arity 7
    • unboxed sums of lifted types up to arity 7

    Ideally we would have levity-polymorphic instances of unboxed tuples and sums.

  • The code generated by -XDeriveLift uses expression quotes instead of generating large amounts of TH code and having special hard-coded cases for some unboxed types.

This implements GHC proposal 47.

Fixes #16384 (closed).

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