Introduce Concrete# for representation polymorphism checks

PHASE 1: we never rewrite Concrete# evidence.

This patch migrates all the representation polymorphism checks to
the typechecker, using a new constraint form

  Concrete# :: forall k. k -> TupleRep '[]

Whenever a type `ty` must be representation-polymorphic
(e.g. it is the type of an argument to a function), we emit a new
`Concrete# ty` Wanted constraint. If this constraint goes
unsolved, we report a representation-polymorphism error to the user.
The 'FRROrigin' datatype keeps track of the context of the
representation-polymorphism check, for more informative error messages.

This paves the way for further improvements, such as
allowing type families in RuntimeReps and improving the soundness
of typed Template Haskell. This is left as future work (PHASE 2).

fixes #17907 #20277 #20330 #20423 #20426

updates haddock submodule

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Metric Decrease:
    T5642
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1 files changed, 17 insertions, 0 deletions

diff --git a/testsuite/tests/rep-poly/T19615.hs b/testsuite/tests/rep-poly/T19615.hs
new file mode 100644
index 0000000000..8d71ca925e
--- /dev/null
+++ b/testsuite/tests/rep-poly/T19615.hs
@@ -0,0 +1,17 @@
+{-# LANGUAGE RankNTypes     #-}
+{-# LANGUAGE PolyKinds      #-}
+{-# LANGUAGE DataKinds      #-}
+{-# LANGUAGE TypeFamilies #-}
+module T19615 where
+
+import GHC.Exts
+
+class Call (r :: RuntimeRep) where
+  type Lev (a :: TYPE r)
+  lift' :: (a :: TYPE r) -> (Lev a -> b) -> b
+  mapF  :: forall r' (a :: TYPE r) (b :: TYPE r'). Call r' => (a -> b) -> Lev a -> Lev b
+
+instance Call LiftedRep where
+  type Lev a = a
+  lift' a k = k a
+  mapF f x = lift' (f x) id