[Sema] Make explicit that resolveInverseType doesn't look through parens

Check for `isParenType` on the TypeRepr to avoid
relying on getting that behavior by casting the
type pointer.

Author: hamishknight

lib/Sema/TypeCheckType.cpp

@@ -5898,14 +5898,17 @@ NeverNullType TypeResolver::resolveInverseType(InverseTypeRepr *repr,
                                                TypeResolutionOptions options) {
   auto subOptions = options.withoutContext(true)
       .withContext(TypeResolverContext::Inverted);
-  auto ty = resolveType(repr->getConstraint(), subOptions);
+  auto *constraintRepr = repr->getConstraint();
+  auto ty = resolveType(constraintRepr, subOptions);
   if (ty->hasError())
     return ErrorType::get(getASTContext());
 
   // If the inverted type is an existential metatype, unwrap the existential
   // metatype so we can look at the instance type. We'll re-wrap at the end.
-  ExistentialMetatypeType *existentialTy =
-      dyn_cast<ExistentialMetatypeType>(ty.get().getPointer());
+  // Note we don't look through parens.
+  ExistentialMetatypeType *existentialTy = nullptr;
+  if (!constraintRepr->isParenType())
+    existentialTy = dyn_cast<ExistentialMetatypeType>(ty.get().getPointer());
   if (existentialTy) {
     ty = existentialTy->getInstanceType();
   }