Don't defunctionalize helpers for class defaults or instance methods

`singletons-th` generates "helper" type families that contain the definitions
of class method defaults or instance methods. For example, this:

```hs
class C a where
  m :: a -> b -> a
  m x _ = x
```

Will be promoted to this:

```hs
class PC a where
  type M (x :: a) (y :: b) :: a
  type M x y = MHelperSym0 `Apply` x `Apply` y

type MHelper :: a -> b -> a
type family MHelper x y where
  MHelper x _ = x

type MHelperSym0 :: a ~> b ~> a
type MHelperSym1 :: a -> b ~> a
...
```

Generating defunctionalization symbols for `MHelper` is wasteful, however, as
we never really _need_ to partially apply `MHelper`. Instead, we can just
generate this code:

```hs
class PC a where
  type M (x :: a) (y :: b) :: a
  type M x y = MHelper x y
```

This takes advantage of the fact that when we apply `MHelper`, we always fully
apply it to all of its arguments. This means that we can avoid generating
defunctionalization symbols for helper type families altogether, which is a
nice optimization.

This patch implements that idea, fixing #608 in the process.

singletons-base/tests/compile-and-dump/Promote/Newtypes.golden

@@ -48,26 +48,5 @@ Promote/Newtypes.hs:(0,0)-(0,0): Splicing declarations
     type TFHelper_0123456789876543210 :: Foo -> Foo -> Bool
     type family TFHelper_0123456789876543210 (a :: Foo) (a :: Foo) :: Bool where
       TFHelper_0123456789876543210 (Foo a_0123456789876543210) (Foo b_0123456789876543210) = Apply (Apply (==@#@$) a_0123456789876543210) b_0123456789876543210
-    type TFHelper_0123456789876543210Sym0 :: (~>) Foo ((~>) Foo Bool)
-    data TFHelper_0123456789876543210Sym0 :: (~>) Foo ((~>) Foo Bool)
-      where
-        TFHelper_0123456789876543210Sym0KindInference :: SameKind (Apply TFHelper_0123456789876543210Sym0 arg) (TFHelper_0123456789876543210Sym1 arg) =>
-                                                         TFHelper_0123456789876543210Sym0 a0123456789876543210
-    type instance Apply @Foo @((~>) Foo Bool) TFHelper_0123456789876543210Sym0 a0123456789876543210 = TFHelper_0123456789876543210Sym1 a0123456789876543210
-    instance SuppressUnusedWarnings TFHelper_0123456789876543210Sym0 where
-      suppressUnusedWarnings
-        = snd ((,) TFHelper_0123456789876543210Sym0KindInference ())
-    type TFHelper_0123456789876543210Sym1 :: Foo -> (~>) Foo Bool
-    data TFHelper_0123456789876543210Sym1 (a0123456789876543210 :: Foo) :: (~>) Foo Bool
-      where
-        TFHelper_0123456789876543210Sym1KindInference :: SameKind (Apply (TFHelper_0123456789876543210Sym1 a0123456789876543210) arg) (TFHelper_0123456789876543210Sym2 a0123456789876543210 arg) =>
-                                                         TFHelper_0123456789876543210Sym1 a0123456789876543210 a0123456789876543210
-    type instance Apply @Foo @Bool (TFHelper_0123456789876543210Sym1 a0123456789876543210) a0123456789876543210 = TFHelper_0123456789876543210 a0123456789876543210 a0123456789876543210
-    instance SuppressUnusedWarnings (TFHelper_0123456789876543210Sym1 a0123456789876543210) where
-      suppressUnusedWarnings
-        = snd ((,) TFHelper_0123456789876543210Sym1KindInference ())
-    type TFHelper_0123456789876543210Sym2 :: Foo -> Foo -> Bool
-    type family TFHelper_0123456789876543210Sym2 (a0123456789876543210 :: Foo) (a0123456789876543210 :: Foo) :: Bool where
-      TFHelper_0123456789876543210Sym2 a0123456789876543210 a0123456789876543210 = TFHelper_0123456789876543210 a0123456789876543210 a0123456789876543210
     instance PEq Foo where
-      type (==) a a = Apply (Apply TFHelper_0123456789876543210Sym0 a) a
+      type (==) a a = TFHelper_0123456789876543210 a a

singletons-base/tests/compile-and-dump/Singletons/BoundedDeriving.golden

@@ -88,78 +88,48 @@ Singletons/BoundedDeriving.hs:(0,0)-(0,0): Splicing declarations
     type MinBound_0123456789876543210 :: Foo1
     type family MinBound_0123456789876543210 :: Foo1 where
       MinBound_0123456789876543210 = Foo1Sym0
-    type MinBound_0123456789876543210Sym0 :: Foo1
-    type family MinBound_0123456789876543210Sym0 :: Foo1 where
-      MinBound_0123456789876543210Sym0 = MinBound_0123456789876543210
     type MaxBound_0123456789876543210 :: Foo1
     type family MaxBound_0123456789876543210 :: Foo1 where
       MaxBound_0123456789876543210 = Foo1Sym0
-    type MaxBound_0123456789876543210Sym0 :: Foo1
-    type family MaxBound_0123456789876543210Sym0 :: Foo1 where
-      MaxBound_0123456789876543210Sym0 = MaxBound_0123456789876543210
     instance PBounded Foo1 where
-      type MinBound = MinBound_0123456789876543210Sym0
-      type MaxBound = MaxBound_0123456789876543210Sym0
+      type MinBound = MinBound_0123456789876543210
+      type MaxBound = MaxBound_0123456789876543210
     type MinBound_0123456789876543210 :: Foo2
     type family MinBound_0123456789876543210 :: Foo2 where
       MinBound_0123456789876543210 = ASym0
-    type MinBound_0123456789876543210Sym0 :: Foo2
-    type family MinBound_0123456789876543210Sym0 :: Foo2 where
-      MinBound_0123456789876543210Sym0 = MinBound_0123456789876543210
     type MaxBound_0123456789876543210 :: Foo2
     type family MaxBound_0123456789876543210 :: Foo2 where
       MaxBound_0123456789876543210 = ESym0
-    type MaxBound_0123456789876543210Sym0 :: Foo2
-    type family MaxBound_0123456789876543210Sym0 :: Foo2 where
-      MaxBound_0123456789876543210Sym0 = MaxBound_0123456789876543210
     instance PBounded Foo2 where
-      type MinBound = MinBound_0123456789876543210Sym0
-      type MaxBound = MaxBound_0123456789876543210Sym0
+      type MinBound = MinBound_0123456789876543210
+      type MaxBound = MaxBound_0123456789876543210
     type MinBound_0123456789876543210 :: forall a. Foo3 a
     type family MinBound_0123456789876543210 @a :: Foo3 a where
       MinBound_0123456789876543210 @a = Apply Foo3Sym0 MinBoundSym0
-    type MinBound_0123456789876543210Sym0 :: forall a. Foo3 a
-    type family MinBound_0123456789876543210Sym0 @a :: Foo3 a where
-      MinBound_0123456789876543210Sym0 = MinBound_0123456789876543210
     type MaxBound_0123456789876543210 :: forall a. Foo3 a
     type family MaxBound_0123456789876543210 @a :: Foo3 a where
       MaxBound_0123456789876543210 @a = Apply Foo3Sym0 MaxBoundSym0
-    type MaxBound_0123456789876543210Sym0 :: forall a. Foo3 a
-    type family MaxBound_0123456789876543210Sym0 @a :: Foo3 a where
-      MaxBound_0123456789876543210Sym0 = MaxBound_0123456789876543210
     instance PBounded (Foo3 a) where
-      type MinBound = MinBound_0123456789876543210Sym0
-      type MaxBound = MaxBound_0123456789876543210Sym0
+      type MinBound = MinBound_0123456789876543210
+      type MaxBound = MaxBound_0123456789876543210
     type MinBound_0123456789876543210 :: forall a b. Foo4 a b
     type family MinBound_0123456789876543210 @a @b :: Foo4 a b where
       MinBound_0123456789876543210 @a @b = Foo41Sym0
-    type MinBound_0123456789876543210Sym0 :: forall a b. Foo4 a b
-    type family MinBound_0123456789876543210Sym0 @a @b :: Foo4 a b where
-      MinBound_0123456789876543210Sym0 = MinBound_0123456789876543210
     type MaxBound_0123456789876543210 :: forall a b. Foo4 a b
     type family MaxBound_0123456789876543210 @a @b :: Foo4 a b where
       MaxBound_0123456789876543210 @a @b = Foo42Sym0
-    type MaxBound_0123456789876543210Sym0 :: forall a b. Foo4 a b
-    type family MaxBound_0123456789876543210Sym0 @a @b :: Foo4 a b where
-      MaxBound_0123456789876543210Sym0 = MaxBound_0123456789876543210
     instance PBounded (Foo4 a b) where
-      type MinBound = MinBound_0123456789876543210Sym0
-      type MaxBound = MaxBound_0123456789876543210Sym0
+      type MinBound = MinBound_0123456789876543210
+      type MaxBound = MaxBound_0123456789876543210
     type MinBound_0123456789876543210 :: Pair
     type family MinBound_0123456789876543210 :: Pair where
       MinBound_0123456789876543210 = Apply (Apply PairSym0 MinBoundSym0) MinBoundSym0
-    type MinBound_0123456789876543210Sym0 :: Pair
-    type family MinBound_0123456789876543210Sym0 :: Pair where
-      MinBound_0123456789876543210Sym0 = MinBound_0123456789876543210
     type MaxBound_0123456789876543210 :: Pair
     type family MaxBound_0123456789876543210 :: Pair where
       MaxBound_0123456789876543210 = Apply (Apply PairSym0 MaxBoundSym0) MaxBoundSym0
-    type MaxBound_0123456789876543210Sym0 :: Pair
-    type family MaxBound_0123456789876543210Sym0 :: Pair where
-      MaxBound_0123456789876543210Sym0 = MaxBound_0123456789876543210
     instance PBounded Pair where
-      type MinBound = MinBound_0123456789876543210Sym0
-      type MaxBound = MaxBound_0123456789876543210Sym0
+      type MinBound = MinBound_0123456789876543210
+      type MaxBound = MaxBound_0123456789876543210
     data SFoo1 :: Foo1 -> Type where SFoo1 :: SFoo1 (Foo1 :: Foo1)
     type instance Sing @Foo1 = SFoo1
     instance SingKind Foo1 where