[torque] Don't emit accessors for indexed fields

I noticed that SeqOneByteString and SeqTwoByteString have generated
functions to get and set their "chars" field which just get or set the
first character in the array. That's unhelpful and potentially
dangerous, so we shouldn't emit these functions.

Change-Id: Iff328fc744e5bd3e70536619d5928df6d959f12f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1890540Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#64693}

src/torque/implementation-visitor.cc

@@ -3166,7 +3166,7 @@ void CppClassGenerator::GenerateClassConstructors() {
 // TODO(sigurds): Keep in sync with DECL_ACCESSORS and ACCESSORS macro.
 void CppClassGenerator::GenerateFieldAccessor(const Field& f) {
   const Type* field_type = f.name_and_type.type;
-  if (field_type == TypeOracle::GetVoidType()) return;
+  if (field_type == TypeOracle::GetVoidType() || f.index.has_value()) return;
   if (!f.name_and_type.type->IsSubtypeOf(TypeOracle::GetTaggedType())) {
     return GenerateFieldAccessorForUntagged(f);
   }