Revert r374202"[ObjC generics] Fix not inheriting type bounds in categories/extensions."

This introduced new errors, see below. Reverting until that can be investigated
properly.

  #import <AVFoundation/AVFoundation.h>

  void f(int width, int height) {
    FourCharCode best_fourcc = kCMPixelFormat_422YpCbCr8_yuvs;
    NSDictionary* videoSettingsDictionary = @{
      (id)kCVPixelBufferPixelFormatTypeKey : @(best_fourcc),
    };
  }

  $ clang++ -c /tmp/a.mm

  /tmp/a.mm:6:5: error: cannot initialize a parameter of type
  'KeyType<NSCopying>  _Nonnull const' (aka 'const id') with an rvalue
  of type 'id'
      (id)kCVPixelBufferPixelFormatTypeKey : @(best_fourcc),
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  1 error generated.

> When a category/extension doesn't repeat a type bound, corresponding
> type parameter is substituted with `id` when used as a type argument. As
> a result, in the added test case it was causing errors like
>
> > type argument 'T' (aka 'id') does not satisfy the bound ('id<NSCopying>') of type parameter 'T'
>
> We are already checking that type parameters should be consistent
> everywhere (see `checkTypeParamListConsistency`) and update
> `ObjCTypeParamDecl` to have correct underlying type. And when we use the
> type parameter as a method return type or a method parameter type, it is
> substituted to the bounded type. But when we use the type parameter as a
> type argument, we check `ObjCTypeParamType` that ignores the updated
> underlying type and remains `id`.
>
> Fix by desugaring `ObjCTypeParamType` to the underlying type, the same
> way we are doing with `TypedefType`.
>
> rdar://problem/54329242
>
> Reviewers: erik.pilkington, ahatanak
>
> Reviewed By: erik.pilkington
>
> Subscribers: jkorous, dexonsmith, ributzka, cfe-commits
>
> Differential Revision: https://reviews.llvm.org/D66696

Author: zmodem

clang/include/clang/AST/Type.h

@@ -5569,7 +5569,7 @@ class ObjCTypeParamType : public Type,
 
 public:
   bool isSugared() const { return true; }
-  QualType desugar() const;
+  QualType desugar() const { return getCanonicalTypeInternal(); }
 
   static bool classof(const Type *T) {
     return T->getTypeClass() == ObjCTypeParam;

clang/lib/AST/Type.cpp

@@ -663,10 +663,6 @@ ObjCTypeParamType::ObjCTypeParamType(const ObjCTypeParamDecl *D,
   initialize(protocols);
 }
 
-QualType ObjCTypeParamType::desugar() const {
-  return getDecl()->getUnderlyingType();
-}
-
 ObjCObjectType::ObjCObjectType(QualType Canonical, QualType Base,
                                ArrayRef<QualType> typeArgs,
                                ArrayRef<ObjCProtocolDecl *> protocols,

clang/test/SemaObjC/parameterized_classes_subst.m

@@ -467,17 +467,3 @@ - (void)mapUsingBlock:(id (^)(id))block {
 - (void)mapUsingBlock2:(id)block { // expected-warning{{conflicting parameter types in implementation}}
 }
 @end
-
-// --------------------------------------------------------------------------
-// Use a type parameter as a type argument.
-// --------------------------------------------------------------------------
-// Type bounds in a category/extension are omitted. rdar://problem/54329242
-@interface ParameterizedContainer<T : id<NSCopying>>
-- (ParameterizedContainer<T> *)inInterface;
-@end
-@interface ParameterizedContainer<T> (Cat)
-- (ParameterizedContainer<T> *)inCategory;
-@end
-@interface ParameterizedContainer<U> ()
-- (ParameterizedContainer<U> *)inExtension;
-@end